The 'Under The Sun' singer was devastated when Ashley Cole's infidelities were revealed and went for tests to make sure she wasn't at risk.
Writing in her new book, 'Cheryl: My Story', she says: "His infidelity had been putting me at risk for a long time. I had to put my mind at rest."
She also tells of her "sadness, physical pain, sickness and fury like I'd never experienced" and revealed her furious rant at Ashley where she shouted "I hope she's worth it. It's the end of your marriage. It's f****d."
Cheryl - who divorced the England soccer player in 2010 following revelations he had cheated on her with a string of women - previously revealed she warned him to leave the UK when her autobiography comes out.
She said: "(I ran some chapters past him) to give him a heads up."
When asked if Ashley wanted any alterations, Cheryl replied: "It wouldn't have mattered if he did, to be quite honest.
"I just thought it would be nice that I gave him the heads up so he can leave the country two weeks before."