The "I Kissed a Girl" singer is planning to imitate Simon Cowell's brand of tough love when she appears as a guest judge on "American Idol" later this month.

The 24-year-old star said: "I might become a little bit of a buddy with Simon, because whenever I watch that show, as much as he's an a**hole, he's a very truthful, honest a**hole."

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"I'm not there to build them up. It's weird, because I don't want to break their hearts, but everyone knows someone who's been doing karaoke and doing little gigs here and there, and nobody has told them that they can't sing on pitch for, like, 15 years?"

"And you're like, 'Someone needs to say something.' And, unfortunately, I might be that gal, to tell you the truth. I always have been."

Katy is not the only celebrity to fill Paula Abdul's vacant chair on the show's judging panel.

Shania Twain and Victoria Beckham have also made one-off appearances.