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
Space and Time (Doctor Who) TARDIS dematerialises while the outer TARDIS (being the same TARDIS) does the same, and the Doctor assures Amy and Rory that they are now back in "normal flight", and then advises Amy to "put some trousers on". "Doctor Who" had previously aired two related specials for Comic Relief. The first was the 1999 spoof "The Curse of Fatal Death", which was also written by Steven Moffat. The spin-off series "The Sarah Jane Adventures" produced its own mini-episode "From Raxacoricofallapatorius with Love" for the 2009 Comic Relief appeal. Unlike "The Curse of Fatal Death", "Space" and "Time" are considered to be