"I was almost horrified when I went back home and watched [Tuesday night's performance show]. It was literally like watching and listening to a whole new show. What you thought was good wasn't very good and what you thought was bad actually was a lot better," said Cowell as a guest on Thursday's broadcast of Ryan Seacrest's KIIS FM radio show.
"[Idol's live finale] is the only opportunity I got to sort of say something publicly, because he's quite a proud man, David. That felt like the right time to say it."
Cowell's apology to Cook came moments before Seacrest revealed home viewers had crowned the 25-year-old Tulsa, OK resident Idol's seventh-season champ over 17-year-old David Archuleta.
"I didn't know at that point who was going to win -- but win or lose, it had to be said," Cowell told Seacrest about the timing of his apology.
An Archuleta vs. Cook finale was both forecasted and anticipated by Cowell, who only predicted Cook as his favorite to take home the title during a Tuesday appearance on The Ellen DeGeneres Show. However during that night's live performance episode he awarded all three rounds to Archuleta and said the teenager scored a "knockout" over Cook.
Cowell told Seacrest he was only thinking of one word when Cook was revealed to be the champ -- "justice."
"I thought it was the right thing," said Cowell. "You always think in a situation like this where someone who's cute like David Archuleta, that it's going to be carried by young girls or grandmothers or [whoever] vote for people like David Archuleta. But actually the person who I thought did the best performances over the 11 or 12 weeks actually deserved to win and he did win. It was good."
In addition, Cowell said he was "actually quite emotional" after Cook was crowned, however he couldn't tell if it was because the seventh-season's resident rocker had won or because the latest installment of the Fox mega-hit had come to a close.
"A bit of both I think," he said with a laugh. "As soon as the announcement [of the winner] comes in, you realize how long its been. It's quite a relief when it's over."