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.

There were enough hints dropped by American Idol regarding this nostalgic performance, but still, it took fans by surprise. Carrie Underwood, who first appeared on the stage 20 years ago as a contestant,