From #FreeBritney to estrangement: Britney Spears is navigating a 'complex' relationship with sons.

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It's been almost two decades since pop star Britney Spears lost a fierce custody battle to her ex-husband, dancer Kevin Federline, which saw her placed on a psychiatric hold.

The pair were married from 2004 to 2007, and share two boys together: Sean Preston Federline, 20, and Jayden James Federline, 19

Now, Federline, 47, has documented that volatile time in his upcoming memoir, You Thought You Knew. In the book, Federline claimed the "proverbial final straw" in his relationship with Spears came when he witnessed the singer allegedly use cocaine while breastfeeding their sons.

Federline alleges that when he confronted Spears over the incident, she threw a drink in his face and stormed off.

Watch: 'Britney Vs Spears' Official Trailer. Post continues after video.

In 2008, Spears' was placed under a conservatorship, which saw the singer's father, Jamie Spears, control her life and finances for 13 years.

Just before the conservatorship began, Federline was granted full custody of their sons.

In 2019, fans and celebrities called for Spears to gain independence, sparking a movement called #FreeBritney. Two years later, a court ended the conservatorship for good.

Federline writes that when Spears regained control over her social media accounts and started making "erratic" posts, her sons stopped using social media altogether, partly in a bid to avoid negativity from her supporters.

He also said the boys' relationship with their mother reached "breaking point" soon after he relocated the family to Hawaii in 2023.

While Federline conceded the #FreeBritney movement may have "started from a good place", he now fears where things are headed.

"All those people who put so much effort into that should now put the same energy into the 'Save Britney' movement. Because this is no longer about freedom. It's about survival," Federline wrote in his memoir.

"This situation with Britney feels like it's racing toward something irreversible. It's become impossible to pretend everything's OK. From where I sit, the clock is ticking, and we're getting close to the 11th hour. Something bad is going to happen if things don't change, and my biggest fear is that our sons will be left holding the pieces."

How Britney Spears responded.

Spears has responded to Federline's allegations on social media and through a representative.

"The constant gaslighting from ex-husband is extremely hurtful and exhausting," the singer wrote on X.

I have always pleaded and screamed to have a life with my boys."

The singer added that "relationships with teenage boys are 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.

"They need to take responsibility for themselves. With one son only seeing me for 45 min in the past 5 years and the other with only 4 visits in the past 5 years. I have pride too. From now on I will let them know when I am available.

"Trust me, those white lies in that book, they are going straight to the bank and I am the only one who genuinely gets hurt here."

Britney Spears shares two sons with Kevin Federline. Image: Getty

The Stronger singer ended her statement by denouncing the tabloids, stressing she "has been trying to live a sacred and private life" since her conservatorship ended.

"I speak on this because I have had enough and any real woman would do the same."

A representative for Spears also shared a statement ahead of the release of Federline's memoir, claiming the dancer was "profiting off" the singer.

"With news from Kevin's book breaking, once again he and others are profiting off her and sadly it comes after child support has ended with Kevin," the representative told PEOPLE.

Spears reportedly paid child support to Federline for 17 years, and made her last payment in November 2024 after her youngest son, Jayden, turned 18.

"All [Britney] cares about are her kids, Sean Preston and Jayden James and their wellbeing during this sensationalism."

Sean Preston and Jayden have only appeared on the red carpet once with their mother; at the July 2013 L.A. premiere of Smurfs 2.

Britney Spears with Sean and Jayden Federline at the Los Angeles premiere of "Smurfs 2". Image: Getty.

In 2023, Spears released her own memoir, called The Woman in Me, and dedicated it to her two boys.

In the memoir, she gave her side of the custody battle, claiming that Federline pushed the false narrative she was "completely out of control".

"He started to say I shouldn't have my kids anymore — at all," Spears wrote. "He not only wouldn't bring them back to me, he wouldn't let me see them for weeks on end."

Things culminated in February 2007, when Spears famously shaved her head.

"After not getting to see the boys for weeks and weeks, Kevin wouldn't let me in. The paparazzi watched it all happen…so that night I gave them some material. I went into a hair salon, and I took the clippers, and I shaved off all my hair," the singer shared.

"Everyone thought it was hilarious. Look how crazy she is! … But nobody seemed to understand that I was simply out of my mind with grief. My children had been taken away from me." 

Feature Image: Getty.