Jennifer Aniston and Justin Theroux have been engaged for many months now. Even as Jen waits for her beau to pop the question, there is talk that Justin has been showing more than a passing interest in Liv Tyler, his co-star in Leftovers.

“Justin and Liv have been racking up a lot of alone time on and off set,” reveals a source and that is, of course, driving Jen crazy.

Things have apparently got worse over the past week with Liv posting photos of herself and Justin on Instagram, and openly talking about his “bulge” during promotional interviews — “There was this scene where he was jogging and there was quite a large bulge in his sweatpants, and it was all over!”

JenA is both livid and jittery, say friends — after all Brad Pitt, her husband of five years, ended their marriage after falling for Angelina Jolie on the sets of Mr and Mrs Smith.