Harry Potter star David Bradley has been cast as the very first Doctor Who in a new TV movie celebrating the 50th anniversary of the cult sci-fi drama. The first image of the actor, who portrayed Hogwarts caretaker Argus Filch in the Potter films, as the late William Hartnell have appeared online and Doctor Who executive producer Steven Moffat has now opened up about film tribute An Adventure in Space and Time, which will debut on the BBC later this year (13). The project chronicles the birth of the Doctor Who franchise and how veteran thespian Hartnell became a TV sensation overnight back in the 1960s. Moffat tells Entertainment Weekly magazine, "It's the story of this unexpected Indian summer William Hartnell had at the end of his career. "He thought he was all washed up, and then suddenly he's this huge star, and he goes through the experience of that and the experience of leaving it." And Moffat feels sure the film will be tough for outgoing Doctor Matt Smith to watch: "It's quite relevant to this time in Doctor Who. I bet Matt Smith will cry when he watches it." Smith announced earlier this summer (13) that he would be handing over the keys to the Tardis to a new time lord when he departs the sci-fi show after it's annual Christmas special in December (13).