Nick Cannon is reportedly writing a tell-all about Mariah Carey.

The 'America's Got Talent' host, who split from the '#Beautiful' hitmaker last summer after six years of marriage, has allegedly signed a lucrative deal with publishers Simon and Schuster because his estranged wife refused to give him $30 million in their divorce settlement.

A source said: ''Mariah was willing to give Nick $10 million but he said 'hell no' and demanded $30 [million]. Mariah says it is what they agreed to in the prenup before they got married.

''Mariah kept telling Nick she was not going to give him a penny more than $10 million. He told her he could write a book and get $30 million and much more for a movie deal for all of the crap she put him through over the years.

''Mariah told Nick nobody cares what he has to say and told him to take it or leave it because that's it - not a penny more. He says she is being unreasonable so he has to do what he has to do.''

The 45-year-old singer, who has three-year-old twins Monroe and Moroccan with Nick, is ''devastated'' that he is planning to betray her.

The insider told MailOnline: ''Now Mariah is angry, devastated and scared that Nick will reveal her inner most secrets and make her look like a desperate fool.''

Nick, 34, who recently started dating model Jessica White, previously insisted he would ''never say anything negative'' about Mariah.

In a post on Twitter in January, he wrote: ''I will never say anything negative about @MariahCarey We are forever a family rooted in love.''