Credit: Jordan Strauss/

Robsten, meet....JenTin?

When Robert Pattinson and Kristen Stewart made their entrance in the garden of L.A.'s SoHo House for Sunday night's afterparty for the MTV Movie Awards, they were followed by another low-key couple: Jennifer Aniston and Justin Theroux!

After weeks of keeping their romance under wraps, the former Wanderlust costars finally went public -- in a big, affectionate way -- at the A-list bash alongside Cameron Diaz, Alex Rodriguez, Reese Witherspoon, Chelsea Handler, Andrew Garfield, Taylor Lautner and many others. See more photos of Jen and Justin.

Chatting with director Brett Ratner, Aniston, 42, and Theroux, 39, were unabashed with each other. She adjusted his tie, and he gave her a sweet kiss, sweetly rubbing her cheek. Wearing a black dress with a short leather jacket, she smiled ear-to-ear and leaned into her man, who rubbed her neck. As they greeted the night's host (and rumored one-time Aniston fling) Jason Sudeikis, a bevy of Hollywood agents and writers plus other celebs, the duo remained at one another's side.

While Aniston chatted animatedly with other guests (including Pattinson, 24), Theroux looked on adoringly, and they exchanged kisses throughout the night. When it was time to leave, Theroux grabbed her booty and stole another kiss!

"Lots of sexual tension," one witness says. "She [has] never seemed happier."