The 'My Life Would Suck Without You' singer - who won the first series of the US TV talent show in 2002 - will appear as a guest judge at an audition next week.
A source said: "Kelly is beyond excited to get back to the show that started it all."
Following The Departure of full-time judge Paula Abdul, who is believed to have quit the show over an alleged pay dispute, a series of famous faces have filled her place - including former Spice Girl Victoria Beckham, hip-hop artist Mary J. Blige and 'I Kissed a Girl' singer Katy Perry.
The source added: "At this stage it doesn't look like Paula will be replaced by one person. The celebrity judges are working really well for now."