Heavily-pregnant Kelly Clarkson is risking a delivery onstage after signing up to appear on the American Idol series finale.

According to Access Hollywood, the talent show's first winner will join another Idol success story, Carrie Underwood, among those returning for the final episode on 7 April (16), but she will be cutting it close to her delivery date.

Clarkson was warned by doctors earlier this year (16) not to attend both an Idol show and the Grammys, so the Since U Been Gone singer opted for the TV talent show over music's big night.

The pop star has already appeared on the programme in a recent episode, offering her thoughts about this season's singers on the 25 February (16) show. During her appearance, the hitmaker struggled with her emotions as she performed on the Idol stage, visibly sobbing while singing her tune Piece by Piece.

“I cried the whole time,” Kelly explained to U.S. talk show host Ellen DeGeneres of her recent onstage breakdown. “I didn’t realise it was gonna be that bad. And we were rehearsing that day and I just couldn’t get through it."

In addition to Clarkson and Underwood, the 7 April (16) finale will feature performances from Idol favourites Ruben Studdard, Fantasia Barrino, Jordin Sparks, Scotty McCreery, Chris Daughtry, Kellie Pickler, Lauren Alaina, and Caleb Johnson.

The big show will wrap up a three-night finale in America, which includes a 90-minute retrospective entitled American Idol: American Dream. Original judges Simon Cowell, Paula Abdul and Randy Jackson will share stories in the thoughtful television special.