Justin Theroux and Jennifer Aniston
Sharpshooter Images/Splash News Online
08/10/2013 at 04:00 PM EDT
He's one popular birthday boy!
, Ben Stiller, Jimmy Kimmel, Tobey Maguire, Laura Dern, John Krasinski
, Don Cheadle, Jason Bateman, Kristen Bell
, Isla Fisher
, Samantha Ronson, Will Arnett, Malin Ackerman and Dax Shepard were among the celebs who headed to Jennifer Aniston
's Bel Air mansion Saturday night as the actress threw her fiancé, Justin Theroux, a 42nd birthday bash
The party also took place on the one-year anniversary of the couple's engagement
. Though the party sparked rumors of a possible surprise wedding, guests dressed down and the atmosphere was casual.
In the afternoon, guests hung outside on the patio of the newly renovated $21 million, 8,500-sq.-ft. home, chatting and listening to pop tunes (Nelly's "Hot in Herre" gets any party started!) before heading inside to toast Theroux.
Aniston's personal chefs prepared appetizer-style food with a relaxed buffet for about 75 guests. On Friday, a large shipment of Champagne had been delivered to the house.
, the We’re the Millers
star, 44, said she was in no rush to get married.
"We just want to do it when it's perfect, and we're not rushed, and no one is rushing from a job or rushing to a job," said Aniston. "And, you know, we already feel married."
Reporting by MELODY CHIU