Kevin Federline ’s upcoming memoir You Thought You Knew is not getting the praise he was antipating as already underperforming on the charts. Sources claim that his publishing advance was just a measly $60,000, a far cry from Britney’s $15 million windfall for The Woman in Me . K-Feds book opened today on Amazon’s best seller list No. 1,126.

However Kevin’s not crying over the small check — because he negotiated 100% of the TV and film rights.

“Kevin knows the book isn’t the jackpot,” says an insider. “He’s playing chess, not checkers. The real money will come when Netflix or Hulu turns it into a limited series.”

Producers are already circling, eager to dramatize the wild Spears-Federline years — custody battles, tabloid wars, and all. “People think they know Kevin and Brit

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