Los Angeles, California - Britney Spears' ex-husband Kevin Federline is releasing a new memoir, and she reportedly isn't taking it too well!

According to Mandatory, the Circus hitmaker isn't happy about Kevin's memoir, You Thought You Knew, and could take legal action against him.

K.Fed announced that his "extremely intimate and transparent" book will hit shelves on October 21, yet insiders shared that Britney is "furious and terrified."

Tipsters claimed that the Toxic singer, who was married to the dancer from 2004 to 2007 and shares two kids with him, is "blindsided" and "livid," adding that he "said nothing when she was paying his bills."

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"But now that the checks stopped, he's ready to talk?" an insider said.

Britney released her own memoir, The Woman in Me, last year, and in it, she revealed that "fame and money" led to the end of her marriage to K.Fed.

The insider continued that the Womanizer singer "thought she was finally healing" after the release of her book, but now she's "back on defense."

They added that Kevin's book "isn't about truth" but instead "about money and relevance," and Britney is apparently "ready to go to war" over it.