Jennifer Aniston and Justin Theroux's Post-Premiere Date Night

By Jennifer Garcia

07/01/2011 at 08:15 PM EDT

They may not have made their red carpet debut together at Thursday's Horrible Bosses premiere in Los Angeles, but Jennifer Aniston's boyfriend Justin Theroux was there to keep her company.

After meeting up inside the premiere, the couple hit Chateau Marmont just past 10 p.m. with a large group of pals, including Aniston's BFF Courteney Cox and Chelsea Handler.

Aniston, 42 – still clad in her Balenciaga dress from the film's premiere – wore Theroux's jacket walking in. Theroux, 39, played the part of dapper boyfriend in a black suit, white shirt – and a clean-shaven face!

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"They were super cute," says an onlooker. "He had his arm around her and kissed her on her cheek. They were whispering in each other's ears."

Theroux seemed to fit in with Aniston's close-knit crew just perfectly. "Everyone seemed to be getting along and in a celebratory mood," adds the source.