The Doctor (Doctor Who) Time Lords a fixed number of twelve regenerations, meaning that every Time Lord had a total of thirteen incarnations including the original. The plot of "The Time of the Doctor" involves the Doctor receiving a new cycle of regenerations from the Time Lords before his expected demise, triggering the regeneration into the Twelfth Doctor, played by Peter Capaldi. The origins of the programme were explored in the docudrama "An Adventure in Space and Time" as part of the 50th anniversary celebrations of "Doctor Who", which starred David Bradley as William Hartnell. Although Time Lords resemble humans, their physiology differs in
Doctor Who (2013 specials) Davies and John Barrowman, with David Tennant's wife Georgia Moffet and their children also guest starring. "The Day of the Doctor" formed the centerpiece of the celebrations, which encompassed programmes across all of the BBC's platforms, including "An Adventure in Space and Time", a "Culture Show" special entitled "Me, You and Doctor Who" presented by Matthew Sweet that explores the wider cultural significance of the show. CBBC broadcast a show called "12 Again" in which past and present stars of the show recounted their memories, Professor Brian Cox delivered a televised lecture on the science of "Doctor Who", and BBC