Justin Timberlake Cheated on Jessica Biel with Olivia Munn

The tabloids broke them up more times anyone could possible count, but they still put up a united front at a recent premiere. Now, word is out that Justin Timberlake cheated on longtime girlfriend Jessica Biel with Olivia Munn.

Though Justin and Jessica walked on the red carpet together at a recent event, things are not as rosy as they would want people to believe, sources say for Us Magazine.

In September this year, Justin was away from Jessica on business – and he chose to spend 3 days romancing Olivia Munn, says an unnamed but reportedly very reliable source.

Admittedly, Justin and Olivia met at a MySpace event on September 26, which is also when they exchanged numbers. After that, Justin never stopped chasing Olivia, one spy claims.

“Munn resisted his advances, telling him it was a no-go if he was still with Biel, 28,” the mag writes. This was how Justin managed to earn her confidence, because he realized which would be the point she would give up at.

Justin “has been telling people it’s over with Jessica, even though the reality is he’s just doing it behind her back,” says the same spy. And he did precisely that with Olivia.

“Believing he had left Biel and that her relationship with Timberlake might develop into something serious, Munn took him to her hotel, the Gansevoort Park Avenue NYC, Sept. 27 and 28, where ‘they were openly affectionate,’ the insider adds,” the mag further says.

What happened afterwards is anyone’s guess but, since the two were never seen together after that, one may as well presume Olivia eventually found out that Justin was still with Jessica.

Contacted for comment, a rep for Timberlake denies the so-called hook-up ever took place, while Munn’s publicist says he won’t address any issue pertaining to his client’s personal life.

The same issue of Us Magazine also promises to reveal how Munn felt “sad” and “used” after the fling, as well as the real reason why Jessica is still with Justin, despite knowing of his wandering eye.