Bieber hinted on Twitter who his "special guest" was, writing, "Who is the living legend that I got on my album?"
"I mean, the fact that I might be singing with one of the greatest voices ever, one of the greatest songs of Christmas ever," he continued. He then tweeted a link to a video message, writing: "Well like I said ... #UnderTheMistletoe is not your normal Christmas album. right @mariahcarey."
In the video, Mariah Carey, who gave birth to twins in May, looked like her normal diva-licous self in graphic leggings, a Marilyn Monroe T-shirt and silver jacket.
"I'm here to tell you a little secret," she said in the video message. "Justin and I are doing a little duet together . My song – All I Want for Christmas which I wrote and produced. I'm very excited about it. You are going to be even more surprised when you hear it. The song sounds great. It will be totally festive!"
The first single from Under the Mistletoe will be a song called "Mistletoe" and will drop on October 18, with the full album released on November 1.
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