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

In his memoir entitled You Thought You Knew, which was released today, Kevin Federline has candidly opened up about his time with Britney Spears.

In one segment, he detailed a drunk call he got from her and some of her friends, RadarOnline.com can reveal.

"I was in Miami for work, trying to stay focused on my commitments, and I got a call," Federline wrote. "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 continued. "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 shared. "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 added. "Not the interviews, not the shows, not the headlines. It was all about them."

In the wake of Federline's book, Spears took to slam 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."