EXCLUSIVE: Britney Spears Ex Kevin Federline Claims Pop Star's Wild Partying With Paris Hilton and Lindsay Lohan Was 'The Final Straw' Before Split — Hope 'Died Right Then'

In his memoir You Thought You Knew, released Tuesday, October 21, Kevin Federline opened up about a shocking drunk dial he received from Britney Spears and some friends that was a breaking point for him, RadarOnline.com can reveal.

"I was in Miami for work, trying to stay focused on my commitments, and I got a call," Federline writes. "It was her, Paris Hilton, and Lindsay Lohan on the line, drunk as hell, begging me to come over. I could hear Preston and Jayden crying in the background. It had to be three or four in the morning. That call was the final straw."

"I'd already seen the photos in the tabloids, the ones of her out with them all night, partying at Paris's Malibu place," he continues. "But hearing my kids crying while she was doing God-knows-what? That was it. Any deep-seated sliver of hope that I'd held onto, that we might still somehow pull it together for the kids, died right then."

Federline noted it "wasn't a one-time thing either" but was part of a "reckless pattern."

"I kept coming across the same stories, the same pictures, the same behavior, over and over," he shares. "She wasn't ready to change, and I couldn't keep waiting for her to figure it out. Every time I started doubting myself, every time it got hard, I replayed those calls in my head, the ones where she was drunk, the ones where I could hear Preston and Jayden crying. That was all the motivation to stay the course."

Federline claimed he put his "head down" and began to prepare for the "fight" of his life – "the fight to be a dad."

"Nothing else mattered anymore," he adds. "Not the interviews, not the shows, not the headlines. It was all about them."

In the wake of Federline's book, Spears took to slamming him on her social media.

"The constant gaslighting from ex-husband is extremely hurtful and exhausting," she said. "I have always pleaded and screamed to have a life with my boys."

"Sadly, they have always witnessed the lack of respect shown by own father for me," she continued. "They need to take responsibility for themselves. With one seeing me for 45 min in the past five years and the other with only four visits in the past five years. I have pride, too. From now on, I will let them know when I am available."