After three seasons at the Blues, the Senegal international has completed a switch to Saudi Arabian side Al Ahli.
Mendy signed for Chelsea from Rennes in 2020 under the old Roman Abramovich ownership, before Todd Boehly and Clearlake Capital completed a takeover two years later.
The new hierarchy's first season at the helm proved to be Mendy's last as a player as he now prepares to compete for Al Ahli.
He took to Instagram to deliver of message of thanks to his fans and teammates, as well as the old owners over the new ones.
"As I prepare to begin a new chapter in my career, it's hard to say goodbye," he said in a statement.
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"It has been an incredible three years wearing the Chelsea jersey, during which we achieved great success, including winning the Champions League, the UEFA Super Cup, and the FIFA Club World Cup.
"I want to sincerely thank Roman [Abramovich], Marina [Granovskaia], Petr [Cech], Christophe [Lollichon], and the entire staff who made it possible for me to represent this prestigious club.
"I am thankful to my coaches and all the staffs for the invaluable lessons and growth I experienced."
However, he did also wish the club best for the future: "Although it's time for me to turn a new page. I sincerely wish the club continued success with the new owners and numerous titles in the years to come."
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Fans were on hand to notice the omission though, with one saying on Twitter: "What a Boehly dig never mentions him."
"No thanks to Boehly hahaha," added another.
A third said: "He said catch that sub Todd Boehly."
Mendy is now one of six players to have left Chelsea this summer as the club begin their rebuild.
Tiemoue Bakayoko's contract expired, with N'Golo Kante and Kalidou Koulibaly following Mendy to Saudi Arabia by signing for Al Ittihad and Al Hilal respectively.
Mateo Kovacic has now completed a transfer to Premier League champions Manchester City, while Kai Havertz has joined Arsenal.