This will mark the first time that Tennant has reprised the role of the Doctor, having portrayed the tenth incarnation of the Time Lord for three series and five specials between 2005 and 2010, while Piper will be making her first appearance as Rose Tyler since the 2010 two part special 'The End of Time'. The duo will also be joined by John Hurt (Alien, Tinker Tailor Soldier Spy), whose role is yet to be revealed.
Prior to today's announcement, the only names that had been confirmed as appearing in the cast of the 3D special were Matt Smith and Jenna-Louise Coleman, who plays the Time Lord's current companion Clara Oswald. Just last week, John Barrowman revealed that he would not be involved in the 50th anniversary show, which has been written by Doctor Who showrunner Steven Moffat and is to be directed by Nick Hurran.
Doctor Who returns to the BBC tonight as the second part of series seven gets underway with 'The Bells of St. John', while the 50th anniversary special will air later in the year after receiving a limited theatrical release in November.