Carrie Underwood gave fans a blast from the past by performing "Alone" on "American Idol," two decades after doing so on the show in 2005.

“American Idol” judge Carrie Underwood has surprised viewers with a callback to her time on the show in 2005.

Carrie Underwood, 42, went back to her “American Idol” roots for the season’s “iconic Idol moments” special on Monday night. For the occasion, the singer — who is now a judge for the singing competition show — chose the exact same dress she wore in 2005 when she won Season 4.