The charity tune - I Know Him So Well - goes on sale in the UK today, and if Sony make it available everywhere, it could raise a lot of money for Comic Relief.
Comedian Kay, 37, and singing sensation Boyle, 49, teamed up for the single, which they sang together on Friday night's Red Nose Day celebrations.
Peter reprised his character Geraldine McQueen from spoof TV show Britain's Got the Pop Factor for the charity single, which is a cover of the original sung by Elaine Paige and Barbara Dickson.