What does Kevin Federline’s upcoming book say about Britney Spears?

The ex-husband of pop star Britney Spears gives new details about the couple’s strained relationship in his new memoir, You Thought You Knew.

Kevin Federline, her one-time backup dancer, paints a picture of Spears’ allegedly erratic behavior as a wife and mother and says he continues to worry about her well-being.

Spears has spoken out against the book, which will be published on Tuesday, and accuses Federline of trying to profit from his relationship with her.

Federline makes a number of accusations against Spears in the memoir, shared with the BBC ahead of the book’s release by Listenin.

He accuses Spears of unhealthy behavior as a mother, including drinking when she was pregnant and taking cocaine while her two sons were still breastfeeding. Spears has previously denied having substance abuse problems.

When they were teenagers, the couple’s sons were afraid of Spears, Federline also claimed. “Sometimes they would wake up in the night to find her standing silently in the doorway watching them sleep – ‘Oh, are you awake?’ — with a knife in her hand,” he wrote. “She would then turn and walk away without explanation.”

Federline also expressed his concern for his estranged ex-wife, writing: “The truth is, this Britney situation feels like it’s racing towards something irreversible. From where I sit, the clock is ticking and we’re approaching the 11th hour.”

He writes that he supported conservatism, where many aspects of Spears’ life were controlled by others for years. Of the Free Britney movement, Federline wrote that he “could never fully get behind it.”

The couple got together in the summer of 2004, after Spears’ publicity peak.

They married a few months later and quickly welcomed their two sons: Preston, now 20, and Jaden, now 19.

Spears filed for divorce in 2006 and the divorce was finalized in 2007.

The couple publicly battled over custody of their sons, and Federline was eventually granted sole custody of the boys.

After Federline was awarded full custody, Spears was seen behaving in a manner that Federline characterized in her book as erratic.

She made headlines with incidents such as shaving her head and hitting a photographer’s car with an umbrella.

These public incidents raised concerns about her mental well-being, and after she was taken to hospital twice, a temporary conservatorship was established in 2008, which became permanent later that year.

Spears remained under this controversial arrangement until 2021, in which her father and others controlled her finances and aspects of her personal life. She did not regain custody of her children until it was revoked.

Spears accused Federline of assaulting her during recent press appearances to promote the book. She describes the content of the memoir as “extremely painful and exhausting” but suggests the work will sell better than her own memoirs.

In that book, The Woman Inside Me, Spears accuses her ex-husband of trying to “convince everyone that I’m completely out of control.”

Spears also defended her relationship with her sons. “I have always begged and screamed to have a life with my boys,” she wrote on social media on Oct. 15, adding that “relationships with teenagers are complicated.”

In a statement to US media, a spokesperson for Spears added: “With the news of Kevin’s book breaking, he and others are once again profiting from it, and unfortunately this comes after Kevin’s alimony ends. All she cares about is her children, Sean Preston and Jaden James, and their well-being during this sensation. She describes her journey in her memoir.”

The BBC has contacted Federline’s lawyer for comment on Spears’ counter-allegations.

While the couple dominated the headlines during their relationship and subsequent divorce, Federline in particular has stayed out of the limelight in recent years. And lately, the spotlight on Spears has largely been on her social media posts.

Federline said he had been thinking about writing a book for many years, but wanted to wait until his children were grown to finish it.

“I picked it up and pretty much put it down for probably a five-year period,” he told The Associated Press. “I think that’s a very good description of who I am, the father that I’ve become, the husband that I am, the ex-husband that I am.”

He also told the AP, “I want my kids to be able to move forward in their lives and know that the real truth of everything is out there.”