Justin Bieber: 'Mistletoe' with Mariah Carey!

Justin Bieber waves the Brazilian flag from his hotel balcony in Rio de Janeiro on Wednesday afternoon (October 5).

The 17-year-old musician even sang to the crowd of fans below. How sweet!

PHOTOS: Check out the latest pics of Justin Bieber

Justin also just revealed the final and very special collaboration on his upcoming holiday album, Under The Mistletoe — Mariah Carey!

Mariah says in a new video, “Justin and I are doing this duet together. It is my song, ‘All I Want For Christmas Is You,’ which I wrote and produced. I think a lot of you are already surprised by this, and you’re going to be even more surprised when you hear it. The song sounds great. I’m very excited for everybody to hear it this Christmas, and to be totally festive with our festive collabo.”

Under The Mistletoe debuts on shelves and online retailers on November 1st. 20+ pics inside…