Here’s everything we know so far:
Cameras caught Pitt at Aniston's star-studded 50th birthday party in Los Angeles on Saturday. The actor tried to avoid being the swarm of paparazzi that were outside of West Hollywood's Sunset Tower, but it looks like one eagle-eyed photographer spotted him.
"Someone extended the invitation to Brad to come to Jen's party and he accepted. He wanted to support Jen and it was a momentous occasion,: an insider tells E! News.
Pitt wasn't the only A-lister in attendance. Aniston celebrated the big 5-0 with her famous pals including Ellen DeGeneres, Sandra Bullock, George & Amal Clooney, Kate Hudson, Katy Perry, Reese Witherspoon, and MORE.
Her former Friends co-stars Courteney Cox and Lisa Kudrow were also there for this big milestone.
"Every single person who loves Jen attended. That included Brad," a source told People. "The party was a celebration of Jen's life. Brad, for long, was a very important part of Jen's life. She debated back and forth with friends if she should invite him."
Were you shocked to hear that Brad attended Jen's birthday party? Let us know in the comments below!