James Corden’s “Carpool Karaoke” has become a fast favourite this year. And unbeknownst to us, when Corden hosted Adele, Lady Gaga, Elton John, and more, he obtained footage of the stars singing Mariah Carey’s “All I Want for Christmas is You.” And of course, he brought in the diva herself to help out. Check it all out! (Photo: Inquisitr)