Harry Potter actor David Bradley has regenerated into the first Doctor Who for a new BBC drama.
An Adventure In Space And Time will tell the story of the sci-fi show's beginnings when William Hartnell was the star of the Tardis.
Hartnell featured in the first series of Doctor Who in November 1963 - a four-part adventure known as An Unearthly Child - until he was replaced by Patrick Troughton in 1966.
Bradley, who played Hogwards caretaker Argus Filch in the Harry Potter films, is joined by Jessica Raine from Call The Midwife and Brian Cox in the new drama.
Waris Hussein, the director of the first ever episode, will be played by Last Tango In Halifax's Sacha Dhawan.
The 90-minute BBC Two drama is part of the 50th anniversary celebrations of the show.
The writer and executive producer of the drama, Mark Gatiss, said: "David Bradley brings every ounce of his talent, humour and presence to the role of William Hartnell. It's a wonderfully touching and subtle performance and I'm immensely proud of both him and the film."
The current Doctor, Matt Smith, will leave the show this year after three series, with his successor expected to appear in the Christmas special.
