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Britney Spears ' ex Kevin Federline is dropping a tell-all which he promises will be "extremely intimate and transparent" -- and fans are not happy.

The tell-all, titled "You Thought You Knew," promises to detail his entire life, from his working-class upbringing to his time as a professional dancer -- and will include the years during his marriage to the Princess of Pop and the accompanying media circus, according to a press release. Gallery Launch Gallery Getty

KF says in the release ... "I achieved my biggest dreams, dealt with crushing heartbreak, and endured constant ridicule, all while becoming the father my children needed as they experienced nonstop emotional turbulence. If you’ve ever had questions, you’ll find answers here."

As you know, the forme

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