Jason Allen Alexander, first husband of Britney Spears, is detailing all the intimate details of his 55-hour marriage to the U.S. pop singer in a new book.

Alexander, who married the "Toxic" singer at a Las Vegas ceremony in 2004, reportedly is writing a tell-all book about the nearly three days he spent married to Spears before the marriage was eventually annulled, US Weekly said.

The 25-year-old admitted that the book, which he claims Spears knows about, also will include details of their sex life.

"Britney knows about it," Alexander claimed. "There are things in the book that will upset her... It does feature having sex with her and what that was like."

In his book, Alexander also offers his opinions of Spears' unsuccessful second marriage to Kevin Federline and the birth of her two children with the aspiring rapper.

"It's best for everyone that Kevin and her have split," he confessed. "She is much more confident now."

"I am really surprised at the speed at which they had kids," he adds, "but it has always been a matter of time."