robert pattinson kristen stewart breaking dawn 2Robert Pattinson and Kristen Stewart kept their on-screen-turned-off-screen romance hush-hush for four years before going (mostly) public with it. But now, in the wake of the world gobbling up Fifty Shades of Grey, OK! magazine claims that another sexy book making its way to shelves will reveal off-the-charts sexy details about Robsten's relationship.

The steamy tell-all -- which may or may not actually or ever exist, of course -- will reportedly focus on the scandalous way the couple got together and how Rob used Nikki Reed to lure Kristen away from her then-boyfriend and supposed "first love" Michael Angarano. There might also be some shocking scoop about the couple's risque sex life. Oooh, scandalous!

A source tells OK!:

When Rob saw he couldn't have Kristen, he went for Nikki — but he never stopped pursuing the lady he really wanted.

Although tongues have wagged in the past about how the two were drawn to one another like magnets from their first meeting, the tell-all reportedly notes that it was during the filming of New Moon that they started to get physical -- and Nikki "ended up hating" Kristen. Ick, I can't stand hearing about a guy driving girls to treat one another with contempt! And this Brenda-Dylan-Kelly love triangle stuff (which we could have guessed on our own anyway) is not exactly the kind of steamy news I'm hoping the book will reveal.

But OK!'s source promises more/better gossip related to Robsten's hot sex life that sounds like it could rival Ana and Christian's:

[Rob and Kristen] are very liberated sexually -- there were even suggestions that they were in an open relationship, so that could come up.

Whaaaa?! Now, see, that's the kind of thing I would never have guessed. Who knows if it's true, but it sure is hot! And let's face it -- when it comes to these two, we'll chug any juice with even with a shred of truth mixed in. They're just that magnetic and intriguing as a couple. (Just look how much they fictional characters played by them inspired E.L. James!) There's no doubt a tell-all like this, if it really exists and has all the steamy details this source is promising, will sell like hotcakes.

In the meantime, enjoy the sexy couple in their element ...

Would you want to read more about Rob and Kristen's risque relationship?