Entertainment Tonight -- Simon Cowell is speaking out to ET about Susan Boyle's refined, new look!

Simon tells ET that he thinks popular scrutiny over Susan's appearance might have caused her to do such things as get a new hairdo, pluck her brows and update her wardrobe.

"I think to be fair, first of all she is a woman, and I think anybody who was subject to the kind of comments is going to go, 'You know what? Maybe I should do something about the way I look,'" he says. "She was probably swooped on by about a million colorists who want to make a name for themselves."

Simon suggests, though, that Susan's once-scruffy looks led him and his fellow judges on "Britain's Got Talent" to be "completely wrong" in their initial impressions of her.

"We were all guilty of judging her before she sang," Simon tells ET. "You watch it back and it is embarrassing. We were completely wrong."

Simon's advice for Susan now? "I am tired now of hearing about the way she looks or the kissing or this or that. Get yourself together, sweetheart, for the big one, which is the semi-finals [of "Britain's Got Talent"]. Chose the right song. Focus yourself. Shut your front door and maybe take a holiday and come back as the person you want to be, not the person you think you should be."

Nonetheless, the big question remains: Is Simon jealous that Susan said she is saving her first kiss for his fellow judge Piers Morgan? "I will be up nights," he deadpans.

Catch "America's Got Talent" when it premieres Tuesday, June 23 at 9 p.m. on NBC.