Selena Gomez & Cara Delevingne are Saint-Tropez Bikini BFF's!

Selena Gomez goes retro with her bikini while celebrating her birthday week on billionaire Alshair Fiyaz‘s new boat Ecstasea on Monday (July 21) in Saint-Tropez, France.

The now 22-year-old actress/singer – happy birthday, Selena! – was joined by a group of gal pals, including Cara Delevingne.

PHOTOS: Check out the latest pics of Selena Gomez

Earlier that day, Selena and Cara were spotted taking a helicopter ride together before boarding the boat. How cool!

15+ pics inside of Selena Gomez and Cara Delevinge hanging out on a yacht together…