SPOILER!!--------From the BBC Doctor Who Site: John Simm will return as the Master in the two special episodes which bring David Tennant's era as the Doctor to a stunning conclusion. There's been speculation about Simm's involvement with the show but we can confirm he'll be back later this year, once again playing the Doctor's deadly nemesis.
Simm first appeared as the Master in Utopia, The Sound of Drums and The Last of the Time Lords. All three episodes were written by Executive Producer and Head Writer Russell T Davies who also wrote his upcoming adventure.
The character debuted in 1971 and on-screen has faced all but the Second and Ninth Doctors. Davies' version of the Master saw him retain his wit and cunning but since Utopia he's been callous and charismatic, sick, psychotic and enormously likeable. In short, everyone's favourite megalomaniac.
At the close of Series Three we saw the Master gunned down by his wife and whilst lying in his enemy's arms, he refused to regenerate. The world believed he had died and the Doctor accepted he was the last of the Time Lords. But this is Doctor Who and you can't keep a good bad guy down!
We've yet to find out how he survived but we can promise we'll be bringing you an exclusive interview with John Simm and some brand new Master material later this year. Stay tuned!