Justin Theroux ditched Jimmy Kimmel's party as soon as Jennifer Aniston arrived

Ah, the perils of having mutual friends.

Jimmy Kimmel is in something of an awkward spot between Jennifer Aniston and Justin Theroux, both close friends of Kimmel and his wife Molly. Over the weekend, Aniston and Theroux were separately invited to a birthday party for Kimmel's son -- but they apparently did not want to cross paths.

Theroux reportedly exited the party as soon as Aniston arrived, according to the Daily Mail, citing a source who claimed Theroux "did look a bit nervous" upon hearing of Aniston's entrance.

"It was obvious that he was alerted to her arrival," the source said.

Kimmel officiated Aniston and Theroux's top-secret 2015 wedding, and he and his wife were among the close friends invited to join the couple on their Bora Bora honeymoon trip. The two couples as well as Howard Stern and his wife Beth were known to often all vacation together.

Despite the tension, it was a very happy occasion at the Kimmel household: The party was for the first birthday of son Billy, who underwent open heart surgery at just three days old at this time in 2017.

Aniston and Theroux announced their breakup in February.