They remained friends throughout his ill-fated relationship with Angelina Jolie.
And eagle-eyed onlookers spotted Brad Pitt, 55, sneaking past the paparazzi as he joined the stars at ex-wife Jennifer Aniston's 50th birthday party in Los Angeles on Saturday night.
Actor Brad, who's reportedly been quietly dating Charlize Theron since January, went incognito in a flat cap as he rushed inside Jennifer's favorite West Hollywood spot, the historic Sunset Tower.
Time to celebrate: Jennifer Aniston partied in style Saturday night as she celebrated her 50th birthday with an exclusive party
Still Friends: Brad Pitt, in flat cap, center, snuck into the star-studded bash, which was held at West Hollywood's Sunset Tower
He wasn't alone, with stars including Katy Perry and boyfriend Orlando Bloom, chat show host Ellen DeGeneres, Gwyneth Paltrow, Barbra Streisand, Jason Bateman and Kate Hudson joining the celebrations.
Jennifer, whose birthday falls on February 11, attended the soirée in eye-catching style, stepping out in a stylish all-black jumpsuit with criss-crossing string backing.
With her golden locks styled in voluminous waves and her makeup applied in typically impeccable style, the star looked relaxed and happy as she was feted by her famous friends, as well as her actor dad John Aniston.
Birthday couture: Jennifer showed up to her own party is a stylish all-black jumpsuit with criss-crossing string backing
As they were: The two are pictured in 2004 at Cannes, a year before they split
Tabloid stars: Brad and Jennifer quickly became the ‘it’ couple of the early 2000s, with their every move making headlines. Two years after they met, Aniston and Pitt married
Still friends: The two divorced in 2005, though they've managed to keep up a cordial relationship in the years since
Also among the attendees was George Clooney, who arrived with his glamorous wife Amal. Jennifer has long been friends with George and visited him and Amal at their lake house in Como last summer.
During an appearance on The Ellen DeGeneres Show, the Friends star revealed how incredible it was to see George become a father.
'It’s amazing to see him with children. That is what we talked about, that anything can happen,' she told the host.
After several years of being celebrated as one of Hollywood's most glamorous couples, Jennifer and Brad shocked fans when they announced that they were divorcing in 2005.
The two began dating after meeting on a blind date their respective agents set up in 1998. They quickly became the ‘it’ couple of the early 2000s, with their every move making headlines.
Two years after they met, Jennifer and Brad tied the knot during a romantic ceremony in Malibu, California. Their marriage ended on January 5, 2005. The couple announced that they had ‘formally’ separated.
It soon emerged that he had begun a relationship with Angelina
