Carrie Underwood is returning to the show that brought her massive success. The country music icon will guest star on a new episode of American Idol in celebration of its 20th season.

Underwood will appear on the broadcast on Sunday (May 15), taking up a role as a mentor. She is expected to coach the Top 5 finalists from Resorts World Las Vegas, which is the home of her Las Vegas residency.

Idol host Ryan Seacrest announced the news of Underwood’s upcoming appearance on Sunday night (May 8) during a special Mother’s Day episode, calling the contestants' anticipated experience a “once-in-a-lifetime mentor session.”

“Well, here’s a dream come true!" a caption reads on American Idol’s official Instagram page. ”Who better to help our hopefuls earn a place in the Grand Finale?"

Indeed, Underwood is an exceptional choice for guiding the remaining contestants through what is likely the toughest and most challenging phase of the competition yet. Not only did she take up the crown for Season 4’s American Idol back in 2005, but she has also scored more than 20 No. 1 hit singles and has earned countless awards and accolades, including eight Grammy wins.

Her upcoming appearance follows recent guest mentors Will.i.am, Gabby Barrett, Derek Hough, Jimmie Allen, Bebe Rexha, Lauren Alaina, Ruben Studdard, Lee DeWyze, Haley Reinhart, David Cook and Jordin Sparks. Underwood's upcoming role on Idol could give HunterGirl and Noah Thompson an edge over the other contestants, as they are the only two country singers remaining in the competition. Only time will tell, though, who will take the title of the next American Idol.

American Idol's next episodes will take place on Sundays on ABC. The winner will be crowned on May 22. Underwood will return to her Reflection: The Las Vegas Residency on May 11. Her ninth studio album, Denim & Rhinestones, is slated for release on June 10.

Country 'American Idol' Stars Who Disappeared

We cheered for them. We voted for them. We followed them. Then, these seven American Idol stars vanished. Or, at least it seems like it.

What happened to some of country music's best American Idol contestants over the last 20 years? This list of country American Idol stars who disappeared includes a winner, a runner-up and a third place finisher, plus several early cuts who enjoyed radio success before losing touch with fans.

PICTURES: See Inside Carrie Underwood's Beautiful Post-'American Idol' Home

Carrie Underwood invested her money wisely after winning American Idol in 2005. One of her first big purchases was a 3,099-square-foot home in the well-to-do Nashville suburb of Franklin, Tenn. Underwood paid $384,000 for a luxurious 3-bedroom, 3.5-bathroom stone and stucco home in a private gated community.

The house features a library, a vaulted ceiling and lovely amenities throughout, but while it's very nice, it's certainly not the kind of home you'd picture for a budding country superstar. Underwood wound up being a huge success right out of the gate with her debut album, Some Hearts, and she sold the home in Franklin for $372,500 in 2007, when she purchased the Brentwood mansion that she would later share with her husband, Mike Fisher.