Accomplished pop stars Avril Lavigne and Katy Perry recently joined on to judge American Idol! The Los Angeles times is reporting that they will split judging duties at the L.A callbacks this January! Other guest judges include Victoria Beckham, Mary J. Blige, Shania Twain, Joe Jonas, Neil Patrick Harris and Kristin Chenoworth. The Idol judges are two of the four performers to have three #1 singles from their debut albums. Lady Gaga and Ace of Bace take the other two spots.