Kevin Federline has claimed Britney Spears cheated on him with a female dancer

Explaining how he, Britney, dancers and other tour staff had enjoyed a "loose, carefree" night on the town before heading back to the hotel in the early hours of the morning, Kevin told how his then-girlfriend suddenly disappeared and he went looking for her.

In an excerpt from his memoir You Thought You Knew shared by USA Today newspaper, he wrote: "Eventually, I decided to check if everything was okay. I stepped into the hallway, our door still cracked, like most on the floor, and headed toward the elevators.

"As I passed one of the rooms, I glanced inside - and froze. There she was. Theresa was sitting on the edge of the bed. Britney stood between her legs, hands on her face, and they were going at it. Full-on making out.

" It was one of those moments that hits you so fast, your brain can't even begin to process it. You just stand there, stunned, not sure what's real. I didn't say a word. Just stood there, watching. For a second, nobody moved. Then they both looked up and saw me, and I turned and walked away."

Kevin fled back to his room and made plans to return to the US before he claimed Britney returned to apologise and urged him not to go.

But he felt the incident marked a "turning point" for their relationship and ultimately brought them closer together.

He explained: "I didn't think about it then, but that moment was a turning point for both of us.

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

"The fact that I was ready to walk away, even after everything I had already given up to be with her, proved it was real. In the days that followed, something seemed to change between us. She became more intentional, more thoughtful about how we were together. It felt like we were truly starting to figure out what we meant to each other."

A spokesperson for Britney - who has sons Sean Preston, 20, and Jayden James, 19, with Kevin - has previously hit out at the book.

Her representative said in a statement: "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.

"All she cares about are her kids, Sean Preston and Jayden James, and their well-being during this sensationalism. She detailed her journey in her memoir."