"Jen and Sandra are new BFFs," the insider tells Us. "They're very excited about the new friendship."
Aniston, 45, got to know Bullock, 49, over a dinner party at mutual pal Gwyneth Paltrow's house. They bonded over many things, likely including their epic, painful divorces (Aniston's from Brad Pitt, Bullock's from Jesse James), and their shared ex-boyfriend Tate Donovan.
Bullock was engaged to Donovan, now 50, in the early 1990s, but the couple split before they had a chance to say "I do." Just a few years later, in the mid-1990s, Donovan—who guest starred on Friends as Rachel Green's love interest Joshua Burgin—presented a ring to Aniston, who ended her relationship with the 24: Live Another Day star in 1998.
"Sandra and Jen have a lot in common and enjoy each other's company," the source adds. "They have been having each other over for dinner regularly."
Earlier this year, the actresses—who also share a friend in Chelsea Handler—were rumored to team up for an upcoming comedy flick with Cameron Diaz, but there has yet to be further confirmation on the supposed plans.