Credit: Stuart Ramson/UN Foundation

American Idol's charity show "Idol Gives Back" returns for the third time tonight, and the special 2-hour episode promises a packed roster of star-studded live performances. This week's Idol mentor Alicia Keyswill join Elton John, Carrie Underwood, Mary J. Blige and the Black Eyed Peas on two different stages (Ryan Seacrest hosts the American Idol stage while Queen Latifah emcees another). The Obamas and Justin Bieber will make pre-taped appearances, and we'll also get a look at charitable work by Idol alumni such as David Cook (pictured during his trip to Ethiopia) and stars like Jennifer Garner."I did a quick taped segment, but Jen is doing a full robust package," Ben Affleck told us. Donations from "Idol Gives Back" benefit Children's Health Fund, Feeding America, Malaria No More, Save the Children and the United Nations Foundation. Make sure to tune in to Fox tonight at 8 p.m. EST/PST—you won't want to miss this!

—Enid Portuguez, with reporting by Kwala Mandel