Credit: Theo Wargo/FilmMagic; Joe Kohen/

Shacking up already!

After reconnecting in March and going public with their romance earlier this month, Jennifer Aniston and new beau Justin Theroux have already taken a bold next step.

"He's living at her place in L.A.!" an insider tells the new Us Weekly, out now. "And she's introducing him as her boyfriend." That's a big deal for Aniston, 42, who hasn't been open about any of her beaus since her 2008 split with John Mayer.

39-year-old Theroux (who usually kept a room at Hollywood's Chateau Marmont before taking up residence at Aniston's posh place) has an apartment in NYC -- and now it's all his, after girlfriend Heidi Bivens recently moved out.

Costume designer Bivens, 35, was Theroux's love for 14 years, and the couple lived together for 6 years. Her rep confirmed to New York Post's Page Six that the suddenly single designer moved out last weekend. (An insider told Us that Aniston and Theroux initially hooked up on the Georgia set of Wanderlust last fal.)

Another insider notes that Bivens is "humiliated" by the recent turn of events.

For more on Aniston and Theroux's fast-track romance, pick up the new Us Weekly, out now.