The former Friends star grew close to Theroux during filming of the romantic comedy in 2010, and they began dating last summer (11).
Rumours suggest a romance sparked up on set, while Theroux was still dating stylist Heidi Bivens, but Aniston is adamant "nothing happened" while they were working.
She tells Good Morning America, "Nothing happened on that movie... That was just a rumour, the easy rumour.
"We were just friends. I’ve known Justin for a long time."