Entertainment Tonight has the latest...

With the news recently revealed that Joe Jonas is now dating actress Camilla Belle, the boy bander's ex Taylor Swift says the '10,000 B.C.' star was the reason for their split.

"They've been together since we broke up," Swift told Us Weekly. "That's why we broke up -- because he met her."

And Taylor, whose song "Always and Forever" is about her breakup with Joe, says that guys should be aware that she may just write about them.

"You know what, if they don't want me to write bad songs about them, they shouldn't do bad things," she says.