Sharon, 60, who was a judge on the show for four years before quitting in 2007, will also expose the backstage rows in a book which will be released in time for Christmas, reported Daily Mirror.
"Sharon knows what this book is going to do and it will be absolutely massive. Sharon has never told the full story about her and Dannii's falling-out. She has spoken a little but for the first time we will hear the full story, along with the detail about Dannii's romance with Simon," a source said.
Sharon is also planning to talk for the first time about the battle to save her 31-year-marriage to Ozzy, 64, which threatened to come to an end earlier this year after he went on a booze-and-drugs binge.