Speaking as part of The Talent Show Story, which starts on Saturday on ITV1, Cowell said he felt "really, really disappointed" that Young had triumphed over Gates in the competition.
"I still to this day can't watch the final back because I was really, really disappointed. I really liked Gareth and wanted him to win," Cowell said. "I remember feeling it in my stomach, I felt sick, that's how much it affected me; it shouldn't but it did."
Quoted in The Sun, Cowell recalls that he found Young to be "obnoxious" during his audition for the show and instantly disliked him, adding that "nothing much has changed".
Young's most recent album, 'Echoes', reached Number One last August. Gareth Gates is currently unsigned.