Looking super-toned in the revealing swimsuit, the actress seemed relaxed and happy as she soaked up the sun with husband Justin Theroux, bestie Courteney Cox and her boyfriend, Johnny McDaid.
Theroux, 45, also flaunted his hot bod and tattoos by going shirtless.
While it may have been her birthday, Aniston didn’t abandon spokeswoman duties, snapped diligently clutching a bottle of Smartwater, as was Cox.
“Jennifer was seen relaxing by the pool and having a good time with her friends while staying hydrated, drinking lots of water,” an eyewitness tells ET. “Jen and Justin were seen holding each other at one point. She seemed to be in a great mood!”
“Jennifer had balloons and what appeared to be a birthday cake,” the onlooker adds.