Ray J alleges Kim Kardashian cheated on her first husband with him.

The singer -- who famously appeared in a sex tape with Kim while he was dating her -- has released a new book about infidelity and in it describes an affair with a married woman who he refers to only as KK, but many sources are alleging is Kim.

In Ray's book, "Death of a Cheating Man: What Every Woman Must Know About Men Who Stray," he writes: "We'd known each other for a while before we dated and there was a mutual attraction, but she was married. She let me know she wanted to get with me.

"She left her husband for me as soon as we started having sex and things between us got intense really fast. After that, I felt obligated to be with her."

Reality TV star Kim has always maintained she never cheated on Damon Thomas, her husband from 2000 to 2004.

In his book, Ray goes on to talk about the highly sexual nature of his relationship with KK.

He adds: "We were like animals; sexually free to try anything, and we did.

"For years KK and I had a great sex life. There was more to our relationship, but the majority of it was about our wild and extreme sexual chemistry. She was a straight freak who was down to do whatever, whenever."

Ray -- who was linked to Whitney Houston before she died -- says his relationship with KK finished because of her jealousy, which included tapping his phone.

Kim has yet to confirm or deny she is the person Ray describes in his book.