Britney Spears ' ex-husband, Kevin Federline , has made chilling accusations that the singer would stand over their sleeping sons with a knife in his upcoming memoir, RadarOnline.com can reveal.

In Federline's book, You Thought You Knew , he described how he's fraught with worry that "something bad is going to happen if things don’t change," regarding his former wife's current mental state. Article continues below advertisement

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The former couple was married from 2004 through 2006 and share two sons: Sean Preston , 20, and Jayden James , 19.

Federline wrote in one chapter of the book, obtained by the New York Times , that as teenagers, his sons were afraid of staying at their mother's home.

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