The pop star was crowned the first-ever Idol in 2002, and she'll be back for the programme's 15th and final season - but this time she'll have a seat at the judges' table, alongside Jennifer Lopez, Keith Urban and Harry Connick, Jr.

"We're really happy she wants to be a part of this," says American Idol executive producer Trish Kinane. "The show has meant a lot to her, and despite being pregnant, she wants to be a part of this."

Clarkson, who is expecting her second child with husband Brandon Blackstock, will serve as a guest judge for this season's first live show, which is scheduled to air in the U.S. on 25 February (16). Due to her pregnancy, she is still unsure whether she will be able to join other Idol alumni at the series finale, which is due to air on 5 and 6 April (16).

Past winners scheduled to participate in duets with this season's finalists are Ruben Studdard, Jordin Sparks, David Cook, Kris Allen, Scotty MCCreery and Nick Fradiani.

Past Idol stars like Studdard, Allen and Clay Aiken have been part of the show's audition rounds, which started airing on TV earlier this month (Jan16). The trio have been offering wannabes tips on how to impress the judges at try-outs across America.