X0202 SCHEDULE 13D/A 0000930413-26-001914 0001345471 XXXXXXXX LIVE 19 Ordinary Shares, $1.50 per share par value 06/30/2026 false 0001274173 G4474Y214 JANUS HENDERSON GROUP PLC

201 Bishopsgate London X0 EC2M 3AE

Brian L. Schorr, Esq. (212) 451-3000 280 Park Avenue 41st Floor New York NY 10017 Y Nelson Peltz AF N X1 0.00 0.00 0.00 0.00 0.00 N 0 IN Y Peter W. May AF N X1 0.00 0.00 0.00 0.00 0.00 N 0 IN 0001345471 N Trian Fund Management, L.P. AF N X1 0.00 0.00 0.00 0.00 0.00 N 13 PN Y Trian Fund Management GP, LLC AF N X1 0.00 0.00 0.00 0.00 0.00 N 0 OO Y Trian Partners AM Holdco II, Ltd. WC N E9 0.00 0.00 0.00 0.00 0.00 N 0 OO Ordinary Shares, $1.50 per share par value JANUS HENDERSON GROUP PLC 201 Bishopsgate London X0 EC2M 3AE This Amendment No. 19 ("Amendment No. 19") amends and supplements the Schedule 13D filed with the SEC on October 2, 2020 as amended by Amendment No. 1, filed on May 12, 2021, as amended by Amendment No. 2 filed on May 19, 2021, as amended by Amendment No. 3 filed on July 19, 2021, as amended by Amendment No. 4 filed on October 4, 2021, as amended by Amendment No. 5 filed on November 16, 2021, as amended by Amendment No. 6 filed on December 13, 2021, as amended by Amendment No. 7 filed on January 6, 2022, as amended by Amendment No. 8 filed on February 1, 2022, as amended by Amendment No. 9 filed on March 9, 2022, as amended by Amendment No. 10 filed on March 31, 2022, as amended by Amendment No. 11 filed on November 15, 2022, as amended by Amendment No. 12 filed on June 2, 2023, as amended by Amendment No. 13 filed on May 2, 2025, as amended by Amendment No. 14 filed on October 27, 2025, as amended by Amendment No. 15 filed on December 22, 2025, as amended by Amendment No. 16 filed on March 24, 2026, as amended by Amendment No. 17 filed on May 12, 2026 ("Amendment No. 17"), and as amended by Amendment No. 18 filed on June 18, 2026 ("Amendment No. 18") (as amended, the "Schedule 13D"), relating to the Ordinary Shares of the Issuer. The address of the principal executive office of the Issuer is 201 Bishopsgate, London, EC2M 3AE United Kingdom. Capitalized terms not defined herein shall have the meaning ascribed to them in the Schedule 13D. Except as set forth herein, the Schedule 13D is unmodified. Items 4, 5, and 6 of the Schedule 13D are hereby amended as follows: Item 4 of the Schedule 13D is hereby amended and supplemented by adding the following: On June 30, 2026, the transactions contemplated by the Agreement and Plan of Merger, dated December 21, 2025 (as amended by Amendment No. 1 to the Agreement and Plan of Merger, dated as of March 24, 2026 and the side letter agreement, dated as of June 16, 2026, the "Merger Agreement"), by and among Parent, Merger Sub and the Issuer were consummated. Pursuant to the Merger Agreement, Merger Sub merged with and into the Issuer (the "Merger"), and the Issuer continued as the surviving company and converted to a private limited company incorporated under the laws of Jersey and changed its name from "Janus Henderson Group plc" to "Janus Henderson Group Ltd.". At the effective time of the Merger (the "Effective Time"), each ordinary share, par value $1.50 per share, of the Issuer (an "Ordinary Share" and collectively, the "Ordinary Shares") outstanding immediately prior to the Effective Time (except for Ordinary Shares held by Parent and as otherwise provided in the Merger Agreement) was converted into the right to receive $52.00 per share in cash, without interest (the "Merger Consideration"). Immediately prior to the Effective Time, Trian Partners AM Holdco II, Ltd. and certain other funds affiliated with Trian Fund Management, L.P. ("Trian") contributed 25,136,205 Ordinary Shares to Jupiter Topco LLC ("Topco") in exchange for equity interests of Topco of equivalent value. All other Ordinary Shares beneficially owned by the Reporting Persons were converted into the right to receive the Merger Consideration. Also immediately prior to the Effective Time, each member of the Issuer's board of directors, including Brian Baldwin and Josh Frank, each a Partner at Trian, resigned from and ceased serving on the Issuer's board of directors. As a result of the Merger, the Ordinary Shares will no longer be listed on The New York Stock Exchange and will be deregistered under Section 12(b) of the Exchange Act. Additionally, as a result of the Merger, the Reporting Persons no longer beneficially own any Ordinary Shares, though each of the Reporting Persons retains an equity interest in the surviving company through its beneficial ownership of equity interests of Topco. Item 5(a) is hereby amended and restated in its entirety as follows: The responses of each of the Reporting Persons with respect to Rows 11, 12 and 13 of the cover pages of this Schedule 13D that relate to the aggregate number and percentage of Ordinary Shares are incorporated by reference herein. Item 5(b) is hereby amended and restated in its entirety as follows: The responses of each of the Reporting Persons with respect to Rows 7, 8, 9, and 10 of the cover pages of this Schedule 13D that relate to the number of shares of Ordinary Shares as to which each of the Reporting Persons has sole or shared power to vote or to direct the vote of and sole or shared power to dispose of or to direct the disposition of are incorporated herein by reference. Item 5(c) is hereby amended and supplemented by adding the following at the end thereof: Except as set forth in Items 4 and 6, which information is incorporated herein by reference, and in Amendment No. 17 and Amendment No. 18, which information is incorporated herein by reference, there have been no new transactions by the Reporting Persons during the sixty days preceding the filing of this Amendment No. 19. Item 5(d) is hereby amended and restated in its entirety as follows: Not applicable. Item 5(e) is hereby amended and restated in its entirety as follows: On June 30, 2026, as a result of the consummation of the Merger, the Reporting Persons ceased to be the beneficial owners of more than five percent of the Ordinary Shares Item 6 of the Schedule 13D is hereby supplemented to incorporate by reference the information set forth in Item 4 above. Nelson Peltz /s/ Nelson Peltz 06/30/2026 Peter W. May /s/ Peter W. May 06/30/2026 Trian Fund Management, L.P. /s/ Peter W. May 06/30/2026 Trian Fund Management GP, LLC /s/ Peter W. May 06/30/2026 Trian Partners AM Holdco II, Ltd. /s/ Peter W. May 06/30/2026