According the BBC Official Site, Dumbledore actor Michael Gambon will be guest starring on the Christmas Special episode of Doctor Who.

The adventure will star Matt Smith as the Doctor, alongside Karen Gillan as Amy and Arthur Darvill as Rory. They’ll be joined by, amongst others, Michael Gambon, one of the industry’s most respected actors who has starred in TV classics such as The Singing Detective and Longitude as well as Academy Award-winning films including Gosford Park and Sleepy Hollow. Recently he has become popular with a new generation, right across the world as Professor Albus Dumbledore in the Harry Potter movies.

ABC News is reporting that:

Billed by screenwriter Steven Moffat as “the most Christmassy Christmas special”, details are nonetheless being kept under wraps by the BBC.The broadcaster has confirmed only that the show will be a “clever twist on Charles Dickens’ Christmas Carol.”