The stunning couple, who made a stellar return to red carpet at the premiere of Theroux's new HBO series The Leftovers on Monday evening, attended the afterparty for the upcoming flick at Tao Downtown, where the two touted their love for each other yet again.
The source says that the duo acted like "they were at their own private party," adding that "they didn't socialize much with other people" and "stayed upstairs."
"Jen and Justin were very intimately talking for what seemed to be a long time," the eyewitness reveals. "They looked very happy together."
The couple's affectionate outing comes just hours after they were photographed looking very much in love at The Leftovers premiere. Not only did Jen and Justin walk the carpet hand-in-hand but they also cuddled for the camera, wrapping their arms around each other's waist.
Theroux looked handsome in a navy suit and white shirt—flashing his megawatt smile with just a hint of scruff—while Aniston rocked a silky black shirt dress, and of course, her diamond engagement ring.
While the happy photos seemingly confirm the couple's blissful relationship status, a second source tells E! News that the longtime pair is doing very well, despite their busy schedules and their commitment to their careers.
But as for the age-old rumor that Aniston is pregnant (which is of course making headlines yet again), the insider insists there's no truth to the baby buzz (shocker!).
Meanwhile, the engaged couple was spotted doing some shopping in NYC on Tuesday. The good-looking duo coordinated their ensembles, both wearing aviator shades, gold watches and all-black attire.
Jen looked casual chic in a pair of cropped pants and a tank top, along with her blingtastic engagement ring, while Justin sported his signature hipster cool style, rocking a pair of skinny jeans and a basic polo.
—Reporting by Sara Kitnick and Michelle Falls