What contestant from Britain's Got Talent was a guest vocalist on Johnny Mathis Christmas album titled Sending you a little Christmas?
Sending You a Little Christmas (album):  In addition to piano accompaniment on the title track by its composer Jim Brickman, this particular holiday release of original recordings (number six for Mathis) is distinguished by duets with guest vocalists Susan Boyle, Natalie Cole, Gloria Estefan, Vince Gill, Amy Grant, Billy Joel, and The Jordanaires. Susan Boyle: Susan Magdalane Boyle (born 1 April 1961) is a Scottish singer who came to international attention when she appeared as a contestant on the TV programme "Britain's Got Talent" on 11 April 2009, singing "I Dreamed a Dream" from "Les Misérables ".
Susan Boyle