Larry Birkhead Larry BirkheadThe gloves have come off.

And it looks like this one's going to court.

Larry Birkhead, aka Anna Nicole Smith's ex, has instructed his lawyer to sue journalist Rita Cosby over allegations in her new book.

In Blonde Ambition: The Untold Story Behind Anna Nicole Smith's Death, Rita claims that Larry and Howard K Stern were caught having sex on camera.

Both Howard and Larry have threatened legal action, but it seems Larry's the first to make his move.

He revealed on Larry King Live : "I've instructed my attorney to sue Rita Cosby and the publisher and any source that spits out that information anywhere.

Anna Nicole SmithAnna Nicole Smith"I would lawyer up if I were them because it's coming their way."