Inside Jennifer Aniston's Star-Studded 50th Birthday -- See the Photo Booth Snaps!

Jennifer Aniston's birthday celebration was quite the A-list affair.

The actress turns 50 years old on Monday, but celebrated early with a celebration at Sunset Tower Hotel in Los Angeles on Saturday night. A who's who of Hollywood was in attendance, including a surprising appearance by her ex-husband, Brad Pitt, as well as George and Amal Clooney, Reese Witherspoon, Robert Downey Jr., Ellen DeGeneres, Katy Perry and more.

A few of Aniston's friends gave a glimpse inside the party, thanks to a fun photo booth set up inside. Gwyneth Paltrow -- who interestingly enough has her own history with Pitt, who's her ex-fiance -- shared her snaps on Instagram on Sunday.

"Happy birthday (last night and tomorrow) to #jenniferaniston our ray of sunshine, example of perpetual goodness," Paltrow wrote. "We love you so much and you make 50 LOOK [fire emoji]."

Kate Hudson also shared photo booth snaps with both Paltrow and Aniston.

"Love these ladies," Hudson wrote. "Celebrated this beauty last night ✨Happy Bday JA! We all love you sooo!"

Aniston was surrounded by her close gal-pals, including jewelry designer Jennifer Meyer, who shared snaps with Aniston surrounded by friends including Sara Foster and Jason Bateman's wife, Amanda Anka.

"Last night celebrating our beautiful Jen ❤️❤️," she wrote. "WE ALL LOVE YOU SO MUCH."

Meanwhile, journalist Derek Blasberg shared snaps featuring Perry and her boyfriend, Orlando Bloom, as well as Aniston's BFF, Courteney Cox.

Makeup artist Gucci Westman was also in attendance -- and Instagrammed a photo booth pic that included Witherspoon -- writing, "Celebrating one of my nearest and dearest last night!! How exciting does Jen make it look to get older ?! 💕❤️."

An eyewitness tells ET that Pitt arrived at his ex-wife's birthday party with his security team. According to the eyewitness, he arrived 45 minutes after Aniston and seemed to be in a "good mood and happy to be there."

When ET spoke to Aniston back in December, she said DeGeneres was actually going to throw her a birthday party. Watch the video below for more:

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