Shania Twain will appear as a celebrity judge on American Idol on Jan. 19 during the series' ninth season. Twain stepped in as a preliminary judge in Chicago in August, along with judges Simon Cowell, Kara DioGuardi and Randy Jackson, as well as host Ryan Seacrest. The ninth season debuts Jan. 12 on the Fox network, with the first four weeks devoted to auditions in various cities. The Hollywood rounds will begin Feb. 9. Other guest judges include Victoria Beckham, Mary J. Blige, Kristin Chenoweth, Neil Patrick Harris, Joe Jonas, Avril Lavigne and Katy Perry.