The two were married from 2000 to 2005.
Brad Pitt is celebrating with his ex-wife!
An eyewitness tells ET that Pitt was seen arriving to Jennifer Aniston's 50th birthday party at the Sunset Tower Hotel in Los Angeles, California, with his security team on Saturday. According to the eyewitness, Pitt arrived 45 minutes after Aniston and seemed to be in a "good mood and happy to be there."
Pitt, 55, tried to keep a low profile as he entered the birthday bash, wearing a hat and a dark shirt as he exited a SUV and made his way inside. Another source tells ET that the father of six went to great lengths not to be seen leaving the party, and that hotel staffers and security helped make it difficult for him to be photographed. Other guests at the party were less concerned about being seen coming and going.
Pitt and Aniston were married from 2000 to 2005. Not long after their breakup, Pitt started dating Angelina Jolie and years later, they were married.
"They are friends," the source said at the time. "They have been friendly back and forth."
“They have each other’s cell phone numbers and communicate from time to time,” the source said. “This is nothing new. Jen and him [Brad] have remained friendly.”
Aniston wasn't Pitt's only ex at the party; Gwyneth Paltrow, Pitt's former fiancee, was also in attendance. The pair were together from 1994 to 1997, three years before Pitt and Aniston tied the knot. Paltrow was stunning at the party, sporting a midi-length sequin dress, tan coat and brown boots.
Aniston herself was also seen at the milestone event, which also attended by Reese Witherspoon, Orlando Bloom, Katy Perry, George and Amal Clooney, Robert Downey Jr. and Jason Bateman.
Just before the party, Dolly Parton told ET's Keltie Knight that she was going to try and make it out to the bash that night. The pair worked together on the Netflix flick, Dumplin', with Parton writing songs and Aniston starring.
"She's having a party [for her 50th birthday]," Parton said. "I've been invited. I'm going to try to go!"
"I'm just going to go to her house and eat her food and drink her wine and say 'Happy Birthday!'" she added of her birthday present to Aniston. "I don't have time to get her a present. I'm busy!"
"No, I'll think of something," Parton later added.
"Well apparently Ellen's throwing me my birthday party," she said. "Yes, she did [tell me that]. And now she has to!"
Observational reporting by Helen Gomez.