First announced on Twitter just after midnight, in the later press release Grant said:
I played Doctor Who in the digital animated Scream Of The Shalka and I'm honoured to be in the Christmas Special.
No information has been released about his role as yet, though the Sun newspaper has suggested that he will play the Doctor's adversary.
An actor with a lengthy career in film and television, Grant is best known for the film Withnail and I in which he starred alongside former Doctor Paul McGann. Grant is not a stranger to Doctor Who either, having played the Doctor himself on two occasions: he first appeared as the "Quite Handsome" Tenth Doctor in the Steven Moffat-penned Comic Relief special The Curse of Fatal Death in 1999; as mentioned above, the actor then had a brief spell as the official Ninth Doctor for the online adventure Scream of the Shalka by Paul Cornell in 2003 - until the television series was announced with Christopher Eccleston at the helm.
The Christmas Special starts filming this week and is directed by Saul Metzstein, who worked on the Blue Peter special, Good as Gold and the first two stories recorded for the next series (Dinosaurs on a Spaceship and A Town called Mercy).
Another actor announced for the Special is Tom Ward, who is best known for playing Harry Cunningham in the series Silent Witness.