Justin Bieber has a special guest on his Christmas album so secret even his producer doesn't know who it is.

The 'Baby' singer has worked with high-profile stars on a series of duets for the festive record - including Busta RhymesBoyz II Men, Usher and The Band Perry - but one special guest so big he's not even told Tricky Stewart, who has been producing most of the tracks, who it is.

Tricky told MTV: "I don't know who's featured on the records. The records, as I know the records - Justin is the artist on the records. I know that he's planning on doing things, but I have no idea what they are."

Rumours as to who the special guest is have included Taylor Swift and Mariah Carey.

As he was recording the album in September, Justin got himself into the Christmas spirit for the LP by decorating the studio with festive decorations.

Tricky added: "Well, it's different in the sense that we've been having Christmas and it's not Christmas. It looks and feels like Christmas except when we come out there's no Christmas. You have to imagine. How else can you have Christmas in the middle of September?"

Tricky is now moving onto other projects - leaving Justin to work with producer Kuk Harrell on putting the finishing touches to the record - but he says he feels the album is a natural progression for the star.

He added: "I think it just kind of made sense that I would be involved. I think Justin doing a Christmas album is right on time - I feel that it's almost necessary that he do a great Christmas album and it's really, really good, too."

Justin's first single 'Mistletoe' will be released on October 18 and the album will be released on November 1.

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