Peter Capaldi officially begins his run as the 12th Doctor on Saturday 's 'Doctor Who ' premiere . The new Doctor is very different from the last one . He has a much more serious look, and he seems to be in charge of things rather than just being an observer. Previous Doctor , Matt Smith , makes a surprise cameo .
Peter Capaldi officially begins his run as the 12th Doctor on Saturday 's 'Doctor Who ' premiere . The new Doctor is very different from the last one . Jenna Coleman 's Clara is a standout in the episode . Previous Doctor , Matt Smith , makes a surprise cameo .