It took place at the Sunset Tower Hotel in Los Angeles. Several of Jen's pals were seen exiting and entering the party, notably Barbra Streisand and James Brolin.
George Clooney and wife Amal Clooney appeared to be in the best of moods when they left the former Friends star's celebration.
The Blast reported that Brad arrived solo in a black escalade and quickly made his way inside.
He was narrowly able to dodge photographers who swarmed his car while he pulled up.
Brad and Jennifer were married from 2000-2005. They announced their separation on January 7, 2005 and were officially divorced on October 2 of that year.
What are your thoughts on Brad showing up to Jen's birthday party? Sound off in the comments!