ROPES & GRAY LLP PRUDENTIAL TOWER 800 BOYLSTON STREET BOSTON, MA 02199-3600 WWW.ROPESGRAY.COM

June 8, 2020 Lisa M. Henry T +1 617 951 7780 Lisa.Henry@ropesgray.com

VIA EDGAR

Securities and Exchange Commission

Division of Investment Management

100 F Street, N.E.

Washington, D.C. 20549

Re: AMG Funds III File Nos. 002-84012 and 811-03752

Ladies and Gentlemen:

On behalf of AMG Funds III (the “Trust”) and pursuant to Rule 497(e) under the Securities Act of 1933, as amended, accompanying this letter for filing are exhibits containing an XBRL interactive data file relating to the supplement, filed with the Securities and Exchange Commission on May 15, 2020 under Rule 497(e) (SEC Accession No. 0001193125-20-144067), to the Prospectus for AMG Managers Cadence Emerging Companies Fund and AMG Managers Cadence Mid Cap Fund, dated October 1, 2019.

The purpose of this filing is to submit an XBRL interactive data file in the manner provided by Rule 405 of Regulation S-T, General Instruction C.3.(g) of Form N-1A, and Rule 497(e).

If you have any questions concerning this filing, please call me at (617) 951-7780.

Sincerely,

/s/ Lisa M. Henry

Lisa M. Henry