Celine will team up with a "virtual" Elvis to sing "If I Can Dream" for the special "American Idol" show.
A source told gossip website TMZ.com: "Celine will sing with a virtual Elvis in the vein of Natalie Cole and Nat King Cole's 'Unforgettable'."
Celine performed the song with an Elvis impersonator during rehearsals last week, but a hologram of "The King" - who died nearly 30 years ago - will allegedly be used for the final performance.
"American Idol" host Ryan Seacrest teased: "Two of the biggest stars in musical history will come together. This duet will have to be seen to be believed."
The remaining "American Idol" contestants will join Celine and Elvis as backing singers. The finalists will also perform "American Prayer" - a song written by Bono and Dave Stewart to raise awareness about AIDS in Africa.
The special two-hour show, which will raise money to fight poverty in the US and Africa, will also feature former "American Idol" winners Kelly Clarkson and Carrie Underwood, Gwen Stefani, Pink, Hugh Grant, Keira Knightley, Jack Black, Helen Mirren, Annie Lennox and Wind and Fire.
The event, hosted by Ellen DeGeneres, will feature performances from the "American Idol" stage and the Los Angeles' Walt Disney Concert Hall.
