Kevin Federline's Memoir 'You Thought You Knew': Biggest Bombshells

Kevin Federline has no problem spilling all the secrets he has been holding onto in his memoir, You Thought You Knew.

In his first-ever tome, out on October 21, Federline has chronicled every aspect of his relationship with Britney Spears — including the steamy details of their first encounter.

According to the 47-year-old DJ, he had no idea who the "Toxic" singer was until they crossed paths at the Hollywood nightclub Joseph's in April 2004.

"We talked for a little while and then hit the dance floor," he wrote in his book. "Nothing too wild, just a little playful back and forth. Honestly, at the time, in my 25-year-old mind, I was just thinking about smashing that."

After their first meeting, they went to the Beverly Hills Hotel, where they reportedly spent time together by the hot tub while their friends hung out in the pool. A few moments later, Spears allegedly grabbed his arm and led him into her private bungalow.

"As soon as we got into the bungalow, Britney turned around, slipped off her underwear and started kissing me, tearing at my clothes with both hands," Federline recalled. "We stumbled toward the bed while I struggled to kick my pants off my ankles."

He added, "What happened between us that night was purely physical. It felt like we were feeding off each other's energy, caught in this whirlwind of chemistry and connection. Very passionate, very intense."

Federline was engaged to Shar Jackson, who was pregnant with their second baby at the time, when he had an intimate first encounter with Spears.

After paparazzi sensed something was brewing between them during a beach outing, he called his pregnant fiancée and told her "about Britney, about the connection [they] had, and how [he] couldn't ignore it."

"I could hear the heartbreak in her voice, and the pain it caused. She was angry. But under the anger was something deeper, a sadness I couldn't undo," he reminisced, noting he should have told Jackson how unhappy he was in their relationship.

Federline shared in his memoir, "I let things unravel instead of facing them head-on. I told myself the distance would make things easier, but it just delayed the inevitable. By the time we spoke, it was too late. I had already let her piece together the truth on her own. The photos of Britney and me on the beach helped."

The "…Baby One More Time" songstress was in the middle of the European leg of her 2004 Onyx Tour when Federline caught her on bed with a female dancer.

"Britney stood between her legs, hands on her face, and they were f------ going at it. Full-on making out," Federline, who admitted to "already catching real feelings" for Spears at the time, wrote in his memoir. "It was one of those moments that hits you so fast, your brain can't even begin to process it."

After seeing the scene, he walked out of the room to book a flight back home. However, Spears "started apologizing" and told him she had no idea how serious Federline was about their romance.

According to the dancer, Spears was "overwhelmed" and admitted it "had been a mistake."

"It was our first fight, or whatever you want to call it. I think it was the moment she realized I wasn't there for the fame or the perks. I was only there for her," he continued.

Federline and Spears tied the knot less than three months after they began dating.

In You Thought You Knew, the You Got Served star recalled how they talked about getting engaged while they were returning to the U.S. following the European leg of Spears' tour.

"There we were, sitting in first class, sipping cocktails, talking about life, and then — bam — she was casually, or maybe not so casually, proposing to me," he wrote. "I kind of laughed it off, played it cool, and told her no."

They did not bring up the topic again until she suffered a knee injury in June 2004.

Federline said, "I thought about what she'd said on the plane. I kept replaying it in my head, wondering if I'd made a mistake brushing it off. By the time she was well enough to think about flying again, I finally worked up the nerve to ask her the question she'd asked me weeks earlier."

Before Federline, Spears was married to Jason Alexander and briefly linked to Colin Farrell. The "Womanizer" singer was also in a long-term relationship with Justin Timberlake from 1999 to 2002.

The Britney & Kevin: Chaotic star claimed Spears never really got over the *NSYNC member.

Per Federline, his now-ex-wife called Timberlake on the night before their wedding to settle their "unfinished business."

"I figured she was talking to her mom or her sister, so I went back to the room," he reflected. "When she got back to the room, I could tell she'd been crying. She said she was talking to Justin. She said she needed to call him, to end one chapter of her life before starting a new one."

He noted that, even after their wedding, Spears still "had not fully moved on" that he "could see that part of her heart still had ties to [Timberlake]."

"She might've loved me, but there was always something there with Justin that she couldn't let go of," said Federline. "Being in love with someone still hanging on to someone else — you feel it, even if they don't say it. It's not something you can compete with."

The patriarch recalled an incident when the "Criminal" songstress slapped him while she was holding their first son, Sean Preston Federline, during an argument over his use of marijuana.

"She knew who I was. She married me knowing it. But she was on the warpath, shouting her head off. Then she slapped me. Right in the face. With our son in her arms," he said of the first time "things got physical."

Eight weeks after their second son, Jayden James Federline, was born in September 2006, Britney filed for divorce from Kevin, citing irreconcilable differences.

The Onion Movie star revealed he was in Canada to promote his album Playing With Fire when he learned about his then-wife's divorce filing.

"I got to the studio, went through the usual motions with producers," he detailed. "I knew what to expect, another day answering the same questions, until a producer ambushed me — right before I went live on air — with: 'How do you feel about Britney filing for divorce?' My brain just…froze."

They reached an initial divorce settlement in March 2007 before finalizing the divorce in July of the same year.

Kevin shared the most shocking revelations about his and Britney's children in several parts of his memoir.

In one part of his book, he claimed the mom-of-two gave her most attention to Jayden and neglected Preston.

"I don't doubt she loved them both, but her actions made it clear who came first," Kevin wrote. "Preston carried that pain for years. The night terrors, the need for constant reassurance, the feeling that he wasn't loved as much as his brother — it lingered. Even as he got older and could articulate his feelings, the scars remained."

He also alleged Britney would take Jayden to ride horses and feed him shellfish despite his severe allergies.

"Preston once told me she had punched him in the face," Kevin added.

In addition, the Excess Baggage contestant claimed the "Oops!... I Did It Again" songstress forced her way into his home with "one b--- hanging out of a ripped shirt" and had several "unsettling" visits with their children.

"One night, after another unsettling visit, the boys came home and said, 'We're done. We're not going back,'" he shared in the book. "You could feel the tension in our house evaporate. They weren't bouncing between two worlds anymore."

Kevin expressed his concern for Britney after she began displaying erratic behavior, admitting he fears she might face the same fate as Michael Jackson or Amy Winehouse.

"The truth is, this situation with Britney feels like it's racing toward something irreversible… From where I sit, the clock is ticking, and we're getting close to the eleventh hour," he wrote in his memoir.

Kevin said the #FreeBritney movement "started from a good place," but he noted how ending the conservatorship also led him to "brace for the worst."

"The Free Britney movement got it wrong," he added. "All of 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."