What is the true nature of the relationship between Larry Birkhead and Howard K. Stern? And was there really a secret, backroom deal over Anna Nicole Smith’s baby daughter Dannielynn?

Those are just two of the explosive questions igniting a new firestorm of name-calling and legal threats over former MSNBC reporter Rita Cosby’s new tell-all, “Blonde Ambition,” in which she claims there’s much more to the story of Anna Nicole’s death than was ever told.

Cosby insisted, “We stand 100 percent behind what's in the book,” adding, “The relationship between Larry and Howard, according to witnesses – and again, people who do not know each other – was much more intimate than we ever knew before.”

Cosby contends that their relationship, and an allegedly damaging videotape, may have led to a deal in which Birkhead supposedly received custody of Dannielynn while Stern was allowed to remain as executor of Anna’s will.

“I think the important thing here is that they had a relationship, and they had something on each other,” Cosby said.

She added, “Larry Birkhead had all the cards. He didn't need to fold in this case. He didn't need to keep Howard K Stern as executor – he could have fought it.”

Both Stern and Birkhead vehemently deny the allegations. Larry told “Extra”, “This is nonsense… Rita Cosby’s book is as fictional as ‘Harry Potter.’”

Famed Hollywood private eye John Nazarian, who worked for Stern and also calls him a friend, said the allegations are all about publicity.

“Who knows what her motivation is? Could it be that she wants publicity?” he blasted.

Stern’s layer, Lin Wood, sent a letter to Cosby, saying if the book defames his client, he “will file a libel action against you and your publisher.”

Wood also allegedly sent a threatening letter to the “Today” show, which canceled a scheduled interview with Cosby this morning.

But Cosby isn’t standing down, insisting, “I would hope that Lin Wood and Larry Birkhead and all those people, all their efforts that they're spending on lawsuits and threats of lawsuits and everything else and these nasty letters to people, why don't they spend their time seeking a wrongful death lawsuit in Florida trying to get the answers to this case?”

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