X0609 4 2026-08-24 0001866757 Brilliant Earth Group, Inc. BRLT 0001883360 MAINSAIL GP III, LLC false C/O MAINSAIL MANAGEMENT COMPANY, LLC 500 WEST 5TH STREET, SUITE 1100 AUSTIN TX 78701 false false true false 0001543760 Mainsail Partners III, L.P. false C/O MAINSAIL MANAGEMENT COMPANY, LLC 500 WEST 5TH STREET, SUITE 1100 AUSTIN TX 78701 false false true false 0001570211 Mainsail Co-Investors III, L.P. false C/O MAINSAIL MANAGEMENT COMPANY, LLC 500 WEST 5TH STREET, SUITE 1100 AUSTIN TX 78701 false false true false 0001883293 MAINSAIL INCENTIVE PROGRAM, LLC false C/O MAINSAIL MANAGEMENT COMPANY, LLC 500 WEST 5TH STREET, SUITE 1100 AUSTIN TX 78701 false false true false 0001883367 MAINSAIL MANAGEMENT COMPANY, LLC false C/O MAINSAIL MANAGEMENT COMPANY, LLC 500 WEST 5TH STREET, SUITE 1100 AUSTIN TX 78701 false false true false false Class B Common Stock 2026-08-24 4 J false 16014 A 31848071 I See footnotes LLC Units 2026-08-24 4 J false 16014 A Class A Common Stock 16014 31848071 I See footnotes The reported transaction, which involves a purchase of a limited partner's interest in Mainsail Co-Investors III, L.P. ("MCOI"), may represent a change in the Reporting Persons' pecuniary interest in common units of Brilliant Earth, LLC (the "LLC Units") and shares of Class B common stock held by MCOI. For purposes of Section 16(b), such deemed purchase, for an aggregate consideration of $18,096, could be matchable against the sales reported on August 10, 2026, as reported on the Form 4 filed by the Reporting Persons on August 12, 2026. Accordingly, the Reporting Persons have fully disgorged to the Issuer, the Section 16(b) deemed profit of $2,033. Consists of (i) 31,098,704 shares of Class B common stock (and associated LLC Units) held by Mainsail Partners III, L.P. ("MP III"), (ii) 61,823 shares of Class B common stock (and associated LLC Units) held by Mainsail Incentive Program, LLC ("MIP"), and (iii) 687,544 shares of Class B common stock (and associated LLC Units) held by MCOI. Mainsail GP III, LLC ("GP III") is the general partner of MP III. MCOI is a co-investment vehicle that invests alongside MP III. GP III is the general partner of MCOI. A three member investment committee of GP III acts by a majority vote, with Gavin Turner possessing a veto right, with respect to the voting and dispositive power of the securities held by MP III and MCOI. Mainsail Management Company, LLC ("MMC") is the managing member of MIP, and Gavin Turner is the sole Manager of MMC. Mr. Turner has separately reported the transactions and reported securities reflected in this statement. The Reporting Persons disclaim beneficial ownership of the reported securities except to the extent of their respective pecuniary interests therein. LLC Units (together with one share of Class B common stock for every LLC Unit) are exchangeable for one share of the Issuer's Class A common stock. The reported LLC Units, which were acquired by the Reporting Persons prior to the Issuer's initial public offering, do not expire. /s/ Gavin Turner, Mainsail GP III, LLC 2026-08-26 /s/ Gavin Turner, Mainsail Partners III, L.P. 2026-08-26 /s/ Gavin Turner, Mainsail Co-Investors III, L.P. 2026-08-26 /s/ Gavin Turner, Mainsail Incentive Program, LLC 2026-08-26 /s/ Gavin Turner, Mainsail Management Company, LLC 2026-08-26