John Legend and Andra Day delivered a beautiful duet during Joe Biden's 'Celebration for Change' live streaming fundraiser Sunday night (July 26).The pair traded vocals and harmonized on a cover of Whitney Houston's take of "Greatest Love of All."Legend sat at his piano by a shelf full of awards, while Day sang from a studio setting for the virtual event in support of Democratic presidential candidate Biden.Jay Leno, hosting the fundraiser, said both singers would return for solo performances