The media mogul said his decision to sign up Alesha for his ITV show was partly because he liked her and partly to wound Strictly - which beat The X Factor in the ratings last year - although he insisted such tactical moves were "meant to be in good spirit."
He told The Sun: "My decision to poach her was 70-30 on the fact she was on Strictly and the fact I liked her."
Cowell went on: "When I was in America I'd read about the ratings battles going on here and I did think Strictly were getting a bit smug. They did great. The funny thing was my trailer was next to Bruno Tonioli's in America. I'd see him arriving in LA looking smug. He's a good friend but we were winding each other up. I did have this plan, thinking, 'You're not going to be smiling so much next year if this comes off'. With us and the BBC, I laugh about it, but there is unbelievable rivalry now. They want to be number one, I want to be number one.
"We do what it takes. It's a game - meant to be in good spirit, not supposed to be dirty tricks. We all begrudgingly shake hands when we see each other. You don't do anything for second place.
"But the Alesha thing was kind of fun."
The sixth series of the talent show is returning with a revamped judging panel. Alesha and comedian David Walliams will take their places for the first time and they will be joined by veteran judge Amanda Holden and by Cowell.