The X Factor boss dismissed Boyle's chances as soon as she walked out on stage for her tryout in 2009 because she was wearing a dowdy dress and had a nervous disposition and unbrushed hair.

However, he was stunned at the singer's rendition of I Dreamed a Dream from Les Miserables and admits he kept his initial unkind reaction in the eventual broadcast to illustrate he had been a "horrible person" on the night.

He tells Britain's Radio Times magazine, "It was a turning point for the show and for me actually as a person. It sounds like a cliche but she made me realise that you can't judge a book by its cover. When she came out I remember thinking, 'God, I hope you're not going to sing because I just...' And then it was amazing! I deliberately kept in (the edit of me) looking like a horrible person as a reminder of what can happen."