An insider close to the sitch spilled the tea with Us Weekly, revealing that the celebrity guests were just as shook as we were that he attended. In October, a source told ET that both were doing well following the breakup. "But it didn't seem like that big of a deal to Jen".
"[She did] call him the day after the party to thank him for coming".
Aside from Mayer, another ex of Aniston's also made a surprise appearance at her party: Brad Pitt.More news: MLB owners, players are talking rule changes to invigorate baseball
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"Jennifer is more comfortable in Los Angeles with her close-knit group of friends", one insider said, adding, "But Justin doesn't feel as at home in L.A., nor with Jennifer's friends, he loves NY, and the edgier crowd in the city". Hudson shared photo booth snaps Sunday on Instagram.
Pitt and Aniston were married from 2000-2005.
"Since they split, her friends believe their plan to move forward in life without one another was the best decision for both of them", the source said at the time.
"He was invited, so why shouldn't he go?"
A number of Jen's other famous friends, including Katy Perry, Kate Hudson, Ellen DeGeneres, and Gwyneth Paltrow, were all in attendance. Meanwhile, Pitt and his ex-wife, Angelina Jolie, 43 split in September 2016, when she filed for divorce (the divorce is still ongoing).