The serials The Deadly Assassin (1976) and Mawdryn Undead (1983) established that a Time Lord can only regenerate 12 times, for a total of 13 incarnations.
Serial'erne The Deadly Assassin (1976) og Mawdryn Undead (1983) etablerede at en Tidsherre kun kan regenerere 12 gange, for en total af 13 inkarnationer.