Over the weekend, the actor reportedly attended Jen's holiday party along with many other A-listers, including Tom Hanks and Rita Wilson, Kate Hudson and Danny Fujikawa, Lisa Kudrow and Reese Witherspoon.
"Brad arrived a little after 7 p.m. and most guests started arriving soon after," a source told E! News. "He was among the first arrive and the second to last guest to leave at close around 11 p.m."
In an interesting twist, the actor's ex Gwyneth Paltrow also attended the bash, along with her husband Brad Falchuk.
"It appeared to be a pretty low key casual affair, a gathering of close friends to celebrate the holidays. The guests were all dressed comfortable and fairly casual," the source said, adding that Jen's house was "tastefully decorated" for the affair.
"It was festive and elegant. Caterers must have arrived earlier in the day to set up but it was all ready by the time her guests arrived," the source said. "It was low key and not crowded. It was probably about 50 guests celebrating with her."
Brad and Jen reunited earlier this year, as well, when he attended her 50th birthday party.
"Brad contacted Jen after her mom died, and she was touched that he knew what a difficult time it was," a source told Us Weekly earlier this year.
The duo will likely run into each other in the coming months as both are nominated for awards at the Golden Globes and Screen Actors Guild Awards.
"There's no awkwardness and they are friendly," a source previously told E! "They wish each other the best and are on good terms."
"They've been in touch over the last few years and talk occasionally. If they run into each other they will congratulate each other and exchange pleasantries. They want the best for each other," the source continued. "The past is a long time in the past. They don't talk often but when they do its very warm and positive. It's not as big of a deal to them as it is to everyone around them. There are no issues with being in the same place at the same time."