In the memoir You Thought You Knew to be released on Tuesday, Federline documents his difficult years as husband, ex-husband and co-parent with Spears, who wrote her own memoir in 2023.
Federline's includes some salacious stories and some potentially disturbing details about her behaviour that have already made headlines.
"I want my children to be able to move forward in their lives and know that the actual truth of everything is out there," Federline, 47, told The Associated Press in a Zoom interview, backed by palm trees in Hawaii where he now lives with wife Victoria Prince and their two daughters.
"That's a very, very big part of this for me. And it's really important that I share my story, so they don't have to."
He and Spears' son Preston is now 20 and his brother Jayden is 19. They have little relationship with their mother.
Federline was a 26-year-old backup dancer for other major pop acts when he coupled with Spears in 2004. Their courtship, two-year marriage and divorce took them through one of the most intense celebrity media frenzies in modern history.
He was ruthlessly roasted as a loser hanger-on, especially after releasing his own deeply mocked hip-hop album.
"I wasn't just famous - I was infamous," he writes in the book, which will be released on the new audiobook first platform Listenin.
Federline writes that a "San Andreas-level seismic shift in my reality" followed a few hours after connecting with Spears, when he left the hotel with the pop star and dozens of paparazzi cars followed them.
He describes the night before their wedding, when Spears called her ex Justin Timberlake seeking closure: "She never really got over him. She might've loved me, but there was something there with Justin that she couldn't let go of."
In the memoir, he makes a number of claims about Spears' behaviour including drinking while pregnant and taking cocaine when the boys were still breastfeeding.
Federline writes that Preston told him Spears mercilessly mocked him and once punched him in the face, and that the boys say they would awaken sometimes "to find her standing silently in the doorway, watching them sleep - 'Oh, you're awake?' - with a knife in her hand".
Spears responded with a statement on her social media accounts, saying Federline has engaged in "constant gaslighting".Â
"Trust me, those white lies in that book, they are going straight to the bank and I'm the only one who genuinely gets hurt here," she said, adding that "if you really know me, you won't pay attention to the tabloids of my mental health and drinking".
She also addressed her relationship with her sons:.
"I have always pleaded and screamed to have a life with my boys. Relationships with teenage boys is complex. I have felt demoralised by this situation and have always asked and almost begged for them to be a part of my life. Sadly, they have always witnessed the lack of respect shown by (their) own father for me."
An attorney for Spears did not respond to a request for comment.
Federline writes about growing up in Fresno, California, and finding "my therapy and my purpose" through dance.
He reminisces about his first big tour, with Pink, and working with Aaliyah, Destiny's Child and Michael Jackson. The memoir also details wrestling with John Cena in the WWE and appearing in a self-mocking Super Bowl commercial.
Federline says Preston and Jayden are living on their own as young adults, and have both been working on making music that makes him proud.
He weighs in on Spears' dissolved court conservatorship, saying it was necessary but hurt most of the people involved. He said the fans who fought to free her left an unfortunate legacy.
"The Free Britney movement may have started from a good place, but it vilified everyone around her so intensely that now it's nearly impossible for anyone to step in," he writes.
He says in the book that he wrote it in part as a public plea for her to get more help.
"I've lost hope that things will ever fully turn around," he writes, "but I still hope that Britney can find peace."
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