Susan Boyle's upcoming charity Christmas single is a rendition of O Come, All Ye Faithful, complete with the voice of Elvis Presley.
The Scottish singer told ITV News' Nick Thatcher it is a "great honour" to take part in the digital duet.
The Christmas carol is in conjunction with Save The Children, the charity for which Boyle is an Ambassador. Royalties from the release will go directly to the charity.
Duetting with Elvis was beyond my wildest dreams. And now that this is able to raise moneyand help children is simply fantastic.
The black-and-white video for the song - which shows a "mini" Elvis dancing alongside the singer - was shot at a Glasgow primary school and features children from the Fast programme.
The charity's chief executive, Justin Forsyth, said he hoped the song would "highlight the plight of children around the world".
Simon Cowell saidhe was "proud" of the former Britain's Got Talent star.
In a video message to Boyle, delivered at a press conference, he said:"No-one of all the people I've met has a bigger heart than you".
The single, from Boyle's fifth album, will be released on Sunday December 8.