SC 13D/A

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 4)*

Blackstone Mortgage Trust, Inc.

(Name of Issuer)

Class A Common Stock, par value $0.01 per share

(Title of Class of Securities)

09257W100

(CUSIP Number)

Randall S. Rothschild

The Blackstone Group L.P.

345 Park Avenue

New York, New York 10154

Tel: (212) 583-5000

with a copy to:

Brian M. Stadler, Esq.

Andrew R. Keller, Esq.

Simpson Thacher & Bartlett LLP

425 Lexington Avenue

New York, NY 10017

Tel: (212) 455-2000

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

May 29, 2013

(Date of Event Which Requires Filing of this Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box.  ¨

Note: Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See §240.13d-7 for other parties to whom copies are to be sent.

* The remainder of this cover page shall be filled out for a reporting person’s initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

CUSIP No. 09257W100

1	NAMES OF REPORTING PERSONS BLACKSTONE HOLDINGS III L.P.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (See Instructions) (a)  ¨        (b)  x
3	SEC USE ONLY
4	SOURCE OF FUNDS (See Instructions)     OO
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)     ¨
6	CITIZENSHIP OR PLACE OF ORGANIZATION     Delaware
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH		7	SOLE VOTING POWER     2,460,784
		8	SHARED VOTING POWER     0
		9	SOLE DISPOSITIVE POWER     2,460,784
		10	SHARED DISPOSITIVE POWER     0
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON     2,460,784
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES (See Instructions)     ¨
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)     8.5%†
14	TYPE OF REPORTING PERSON (See Instructions)     PN

† The percentage of shares of Common Stock (as defined below) is calculated assuming 28,801,424 shares of Common Stock outstanding, after giving effect to the Offering (as defined below), based on information reported in the Issuer’s press release dated May 29, 2013 announcing the closing of the Offering and information provided by the Issuer.

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CUSIP No. 09257W100

1	NAMES OF REPORTING PERSONS BLACKSTONE HOLDINGS III GP L.P.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (See Instructions) (a)  ¨        (b)  x
3	SEC USE ONLY
4	SOURCE OF FUNDS (See Instructions)     OO
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)     ¨
6	CITIZENSHIP OR PLACE OF ORGANIZATION     Delaware
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH		7	SOLE VOTING POWER     2,460,784
		8	SHARED VOTING POWER     0
		9	SOLE DISPOSITIVE POWER     2,460,784
		10	SHARED DISPOSITIVE POWER     0
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON     2,460,784
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES (See Instructions)     ¨
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)     8.5%†
14	TYPE OF REPORTING PERSON (See Instructions)     PN

† The percentage of shares of Common Stock is calculated assuming 28,801,424 shares of Common Stock outstanding, after giving effect to the Offering, based on information reported in the Issuer’s press release dated May 29, 2013 announcing the closing of the Offering and information provided by the Issuer.

3

CUSIP No. 09257W100

1	NAMES OF REPORTING PERSONS BLACKSTONE HOLDINGS III GP MANAGEMENT L.L.C.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (See Instructions) (a)  ¨        (b)  x
3	SEC USE ONLY
4	SOURCE OF FUNDS (See Instructions)     OO
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)     ¨
6	CITIZENSHIP OR PLACE OF ORGANIZATION     Delaware
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH		7	SOLE VOTING POWER     2,460,784
		8	SHARED VOTING POWER     0
		9	SOLE DISPOSITIVE POWER     2,460,784
		10	SHARED DISPOSITIVE POWER     0
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON     2,460,784
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES (See Instructions)     ¨
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)     8.5%†
14	TYPE OF REPORTING PERSON (See Instructions)     OO

† The percentage of shares of Common Stock is calculated assuming 28,801,424 shares of Common Stock outstanding, after giving effect to the Offering, based on information reported in the Issuer’s press release dated May 29, 2013 announcing the closing of the Offering and information provided by the Issuer.

4

CUSIP No. 09257W100

1	NAMES OF REPORTING PERSONS THE BLACKSTONE GROUP L.P.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (See Instructions) (a)  ¨        (b)  x
3	SEC USE ONLY
4	SOURCE OF FUNDS (See Instructions)     OO
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)     ¨
6	CITIZENSHIP OR PLACE OF ORGANIZATION     Delaware
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH		7	SOLE VOTING POWER     2,460,784
		8	SHARED VOTING POWER     0
		9	SOLE DISPOSITIVE POWER     2,460,784
		10	SHARED DISPOSITIVE POWER     0
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON     2,460,784
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES (See Instructions)     ¨
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)     8.5%†
14	TYPE OF REPORTING PERSON (See Instructions)     PN

† The percentage of shares of Common Stock is calculated assuming 28,801,424 shares of Common Stock outstanding, after giving effect to the Offering, based on information reported in the Issuer’s press release dated May 29, 2013 announcing the closing of the Offering and information provided by the Issuer.

5

CUSIP No. 09257W100

1	NAMES OF REPORTING PERSONS BLACKSTONE GROUP MANAGEMENT L.L.C.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (See Instructions) (a)  ¨        (b)  x
3	SEC USE ONLY
4	SOURCE OF FUNDS (See Instructions)     OO
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)     ¨
6	CITIZENSHIP OR PLACE OF ORGANIZATION     Delaware
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH		7	SOLE VOTING POWER     2,460,784
		8	SHARED VOTING POWER     0
		9	SOLE DISPOSITIVE POWER     2,460,784
		10	SHARED DISPOSITIVE POWER     0
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON     2,460,784
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES (See Instructions)     ¨
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)     8.5%†
14	TYPE OF REPORTING PERSON (See Instructions)     OO

† The percentage of shares of Common Stock is calculated assuming 28,801,424 shares of Common Stock outstanding, after giving effect to the Offering, based on information reported in the Issuer’s press release dated May 29, 2013 announcing the closing of the Offering and information provided by the Issuer.

6

CUSIP No. 09257W100

1	NAMES OF REPORTING PERSONS STEPHEN A. SCHWARZMAN
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (See Instructions) (a)  ¨        (b)  x
3	SEC USE ONLY
4	SOURCE OF FUNDS (See Instructions)     OO
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)     ¨
6	CITIZENSHIP OR PLACE OF ORGANIZATION     United States of America
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH		7	SOLE VOTING POWER     2,460,784
		8	SHARED VOTING POWER     0
		9	SOLE DISPOSITIVE POWER     2,460,784
		10	SHARED DISPOSITIVE POWER     0
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON     2,460,784
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES (See Instructions)     ¨
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)     8.5%†
14	TYPE OF REPORTING PERSON (See Instructions)     IN

† The percentage of shares of Common Stock is calculated assuming 28,801,424 shares of Common Stock outstanding, after giving effect to the Offering, based on information reported in the Issuer’s press release dated May 29, 2013 announcing the closing of the Offering and information provided by the Issuer.

7

This Amendment No. 4 (“Amendment No. 4”) to Schedule 13D relates to the class A common stock, par value $0.01 per share (“Common Stock”), of Blackstone Mortgage Trust, Inc., a Maryland corporation (the “Issuer”), and amends and supplements the initial statement on Schedule 13D filed on December 21, 2012 (the “Schedule 13D”), as amended and supplemented by Amendment No. 1 to Schedule 13D filed on March 27, 2013, Amendment No. 2 to Schedule 13D filed on May 8, 2013 and Amendment No. 3 to Schedule 13D filed on May 20, 2013. Capitalized terms used but not defined in this Amendment No. 4 shall have the same meanings ascribed to them in the Schedule 13D.

Item 4. Purpose of the Transaction.

Item 4 of the Schedule 13D is hereby supplemented as follows:

On May 29, 2013, the Issuer sold an aggregate of 25,875,000 shares of Common Stock (including 3,375,000 shares sold to the underwriters upon full exercise of the underwriters’ over-allotment option) (the “Offering”) to a syndicate of underwriters in a firm commitment underwritten offering. Holdings III purchased 1,960,784 shares of Common Stock for an aggregate purchase price of $50.0 million in the Offering at the public offering price of $25.50 per share.

Item 5. Interest in Securities of the Issuer.

Item 5 of Schedule 13D is hereby amended and restated as follows:

(a) – (b) As of the date hereof, Blackstone Holdings III directly holds 2,460,784 shares of Common Stock.

Blackstone Holdings III GP L.P. is the general partner of Blackstone Holdings III. Blackstone Holdings III GP Management L.L.C. is the general partner of Blackstone Holdings III GP L.P. The Blackstone Group L.P. is the managing member of Blackstone Holdings III GP Management L.L.C. Blackstone Group Management L.L.C. is the general partner of The Blackstone Group L.P. Blackstone Group Management L.L.C. is wholly owned by its senior managing directors and controlled by its founder, Stephen A. Schwarzman. Each of the Blackstone entities and Mr. Schwarzman may be deemed to beneficially own the shares of Common Stock beneficially owned by Blackstone Holdings III.

The aggregate number and percentage of the shares of Common Stock beneficially owned by each Reporting Person and, for each Reporting Person, the number of shares as to which there is sole power to vote or to direct the vote, shared power to vote or to direct the vote, sole power to dispose or to direct the disposition, or shared power to dispose or to direct the disposition are set forth on rows 7 through 11 and row 13 of the cover pages of this Schedule 13D and are incorporated herein by reference. The percentage of shares of Common Stock beneficially owned by each Reporting Person set forth on the cover pages of this Schedule 13D is calculated assuming 28,801,424 shares of Common Stock outstanding, after giving effect to the Offering, based on information reported in the Issuer’s press release dated May 29, 2013 announcing the closing of the Offering and information provided by the Issuer.

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Neither the filing of this Schedule 13D nor any of its contents shall be deemed to constitute an admission that any of the Reporting Persons (other than Blackstone Holdings III, which directly holds the shares of Common Stock reported on this Schedule 13D) is the beneficial owner of the Common Stock referred to herein for purposes of Section 13(d) of the Securities Exchange Act of 1934, as amended, or for any other purpose, and such beneficial ownership is expressly disclaimed.

(c) Except as set forth herein, none of the Reporting Persons has engaged in any transaction since the most recent filing of Schedule 13D filed on May 20, 2013.

(d) Not applicable.

(e) Not applicable.

Item 6. Contracts, Arrangements, Understandings or Relationships With Respect to Securities of the Issuer.

Item 6 of the Schedule 13D is hereby supplemented as follows:

Holdings III previously entered into a Lock-Up Agreement, dated as of March 26, 2013, a copy of which was filed as Exhibit 6 to Amendment No. 1 to Schedule 13D filed by the Issuer on March 27, 2013 and incorporated herein by reference. In connection with the Offering, pursuant to the requirements of the Financial Industry Regulatory Authority, Inc., Holdings III entered into an additional lock-up agreement, dated as of May 29, 2013 (the “Offering Lock-Up Agreement”) pursuant to which it agreed that, until 180 days after the May 22, 2013 effectiveness of the Issuer’s Registration Statement on Form S-11 (File No. 333-187541) it will not dispose of or hedge the Common Stock.

The description of the Offering Lock-Up Agreement contained in this Item 6 is not intended to be complete and is qualified in its entirety by reference to such agreement, which is filed as an exhibit hereto and incorporated by reference herein.

Item 7. Material to be Filed as Exhibits.

Item 7 of Schedule 13D is hereby supplemented as follows:

10. Additional Blackstone Mortgage Trust, Inc. Lock-Up Agreement dated as of May 29, 2013 of Blackstone Holdings III L.P.

9

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Dated: May 31, 2013

BLACKSTONE HOLDINGS III L.P.
By:	Blackstone Holdings III GP L.P., its general partner
By:	Blackstone Holdings III GP Management L.L.C., its general partner
By:	/s/ John G. Finley
Name:	John G. Finley
Title:	Chief Legal Officer
BLACKSTONE HOLDINGS III GP L.P.
By:	Blackstone Holdings III GP Management L.L.C., its general partner
By:	/s/ John G. Finley
Name:	John G. Finley
Title:	Chief Legal Officer
BLACKSTONE HOLDINGS III GP MANAGEMENT L.L.C.
By:	/s/ John G. Finley
Name:	John G. Finley
Title:	Chief Legal Officer
THE BLACKSTONE GROUP L.P.
By:	Blackstone Group Management L.L.C., its general partner
By:	/s/ John G. Finley
Name:	John G. Finley
Title:	Chief Legal Officer

10

BLACKSTONE GROUP MANAGEMENT L.L.C.
By:	/s/ John G. Finley
Name:	John G. Finley
Title:	Chief Legal Officer
/s/ STEPHEN A. SCHWARZMAN
STEPHEN A. SCHWARZMAN

11

EX-99.10

Exhibit 10

Blackstone Holdings III, L.P.

Additional Lock-Up Agreement

May 29, 2013

Citigroup Global Markets Inc.

Merrill Lynch, Pierce, Fenner & Smith

    Incorporated

J.P. Morgan Securities LLC

c/o Citigroup Global Markets Inc.

388 Greenwich Street

New York, New York 10013

Additional Blackstone Mortgage Trust, Inc. Lock-Up Agreement

Ladies and Gentlemen:

WHEREAS, this letter agreement (this “Agreement”) relates to the proposed public offering (the “Offering”) by Blackstone Mortgage Trust, Inc., a Maryland corporation (the “Company”), of its class A common stock, $0.01 par value per share;

WHEREAS, , Blackstone Holdings III, L.P. (“Blackstone Holdings”) is the holder of 500,000 shares of Class A common stock purchased from the Company in connection with a private offering of the Company’s Class A common stock in December 2012;

WHEREAS, Blackstone Holdings anticipates purchasing up to an additional $50 million of class A common stock in the Offering (these shares as well as the 500,000 shares purchased in December 2012 are collectively referred to as the “Common Stock”);

WHEREAS, in order to induce you and the other underwriters for which you act as representative (“Underwriters”) to underwrite the Offering, Blackstone Holdings has agreed in a separate lock-up agreement (the “Initial Lock-Up Agreement”) that, without the prior written consent of each of Citigroup Global Markets Inc., Merrill Lynch, Pierce, Fenner & Smith Incorporated and J.P. Morgan Securities LLC, it will not sell, transfer or otherwise dispose of any shares of the Company’s class A common stock during the period beginning on the date of the Initial Lock-Up Agreement until one hundred eighty (180) days from the date of the final prospectus for the Offering; and

WHEREAS, the Common Stock has been deemed by the Corporate Finance Department of the Financial Industry Regulatory Authority, Inc. (the “FINRA”) to be underwriting compensation received by the Underwriters in connection with the Offering and Blackstone Holdings and Blackstone Advisory Partners LP (“Blackstone”), a participating member in the Offering, desire to enter into this Agreement in order to comply with FINRA Conduct Rule 5110(g)(1), which Agreement is in addition to, and not a limitation of, the Initial Lock-Up Agreement;

NOW, THEREFORE, for good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged Blackstone Holdings and Blackstone hereby agree as follows:

1. The Common Stock will not be sold during the Offering.

2. During the period from the date hereof until one hundred eighty (180) days immediately following the date of effectiveness of the Offering or commencement of sales of the Offering (“Lock-Up Period”), Blackstone Holdings and Blackstone certify that Blackstone Holdings (a) will not, directly or indirectly, offer, sell, agree to offer or sell, solicit offers to purchase, grant any call option or purchase any put option with respect to, transfer, assign, pledge, hypothecate, borrow or otherwise dispose of the Common Stock, and (b) will not establish or increase any “put equivalent position” or liquidate or decrease any “call equivalent position” with respect to the Common Stock (in each case within the meaning of Section 16 of the Securities Exchange Act of 1934, as amended, and the rules and regulations promulgated thereunder), or otherwise enter into any hedging, short sale, swap, derivative, put or call or other transaction or arrangement that transfers to another, in whole or in part, any economic consequence of ownership of the Common Stock or results in the effective economic disposition of the Common Stock by the undersigned, whether or not such transaction is to be settled by delivery of Common Stock, other securities, cash or other consideration.

3. Notwithstanding the foregoing, this Agreement shall not prohibit the following during Lock-Up Period:

(a) transfers of the Common Stock by operation of law;

(b) transfers of the Common Stock by reason of reorganization of the Company; or

(c) transfers of the Common Stock to any of the Underwriters and any officer or partner thereof provided that any such transferee executes and delivers to Citigroup Global Markets Inc. (“Citigroup”) an agreement satisfactory to Citigroup certifying that such transferee is bound by the terms of this Agreement for the reminder of Lock-Up Period;

4. Blackstone Holdings and Blackstone hereby represent and warrant that each has full power and authority to enter into this Agreement and that this Agreement constitutes the legal, valid and binding obligation of each, enforceable in accordance with its terms. Upon request, Blackstone Holdings and Blackstone will execute any additional documents necessary in connection with enforcement hereof. Any obligations of Blackstone Holdings and Blackstone shall be binding upon their successors and assigns from the date first above written.

5. This Agreement shall terminate and be of no further force and effect in the event that: (a) prior to the execution of the Underwriting Agreement by the Company, the Company notifies Citigroup in writing that the Company has determined not to

proceed with the Offering; or (b) after the execution of the Underwriting Agreement by the Company, the Company has not consummated the Offering within 60 days after the termination of the Underwriting Agreement.

6. In the event of any inconsistency between this Agreement and the Initial Lock-Up Agreement, the provisions of this Agreement shall control.

This Agreement shall be governed by and construed in accordance with the laws of the State of New York. Delivery of a signed copy of this letter by facsimile transmission shall be effective as delivery of the original hereof.

Very truly yours,
BLACKSTONE HOLDINGS III L.P.
By:	/s/ Stephen Plavin
Print Name:	Stephen Plavin

BLACKSTONE ADVISORY PARTNERS L.P.
By:	/s/ Thomas Morrison
Name:	Thomas Morrison
Title:	Authorized Signatory