@drwhofilmingSmith cut his hair earlier this year before travelling to America to film Ryan Gosling's 'How to Catch a Monster'. Fans have speculated for months whether his hair will have grown back in time for filming his final story. Smith was most recently seen at the GQ Men of the Year Awards yesterday with the same short haircut, casting further doubt that Smith would appear in the special with his regular 'do.
Matt Smith has confirmed this morning that he will start shooting the Christmas Special on Sunday. And be wearing a wig :)
The 2013 Christmas special will be broadcast on the 25th December, and will mark the first appearance of Peter Capaldi as the Twelfth Doctor.