Robert Pattinson and Kristen Stewart keep their relationship on the down low, but their sex life is wild and swinging. It’s almost an open relationship, according to a new tabloid report.

The details are about to be exposed in a new tell-all book. Believe it?

“It’s going to be a very juicy read,” a source tells OK! magazine, one of the least reliable gossip tabloids on the magazine rack.

“One big topic will be how they first got together. Rob basically stole Kristen from first love, [actor] Michael Angarano, and used castmate Nikki Reed along the way.

“When Rob saw he couldn’t have Kristen he went for Nikki — but he never stopped pursuing the lady he really wanted,” the source says.

Rob and Kristen reportedly also have a secret crazy sex life,” according to HollywoodLife, which basically regurgitates the story without any effort to substantiate it.

“They are very liberated sexually — there were even suggestions that they were in an open relationship, so that could come up,” a source tells the mag. “And of course their love of partying could be a topic. The book could get to the bottom of all the rumors once and for all.”

Unfortunately, the article doesn’t mention either an author or publisher. As for their sex life, how could anybody know about that except the two people in the room? And if it were wild and crazy, doesn’t it seem likely it would have leaked by now?

The most certainly have a sex life, but unless they’re having threesomes or attending orgies, the phantom author will have a hard time getting the facts. But that’s no problem for OK or HollywoodLife.