Theroux popped the question to the former Friends star with an eight carat diamond ring during his 41st birthday celebrations in New York City on 10 August (12) - and she said yes.
Notoriously tight-lipped Aniston recently gushed about her new fiance on her pal's U.S. late night show Chelsea Lately, and now she confesses Theroux's decision to take their relationship to the next level came as a total surprise.
She tells People magazine, "(The proposal) was one of the sneakiest jobs I've ever seen. I had no idea."
And the 43 year old reveals the actor picked out her sparkler all by himself: "I didn't know what I wanted for a ring. He just knows what I like."