Doctor Who boss Steven Moffat has said he struggles with deciding when it is time for the Time Lord to regenerate because he gets so attached to each actor who takes the role.
The BBC series writer and executive producer told The Sun that it was always a tough decision to wave goodbye to an incarnation of the Doctor.
He said: "One of the hardest things to notice is when your new idea has become your old idea and it's time to get rid of it."
Peter Capaldi has taken over the character from outgoing Doctor Matt Smith for the upcoming series of the hit BBC show.
Steven also promised that Peter's version of the role would have "a bit more gravity", saying that he thought with previous Doctor Matt's portrayal "some of the humour was getting a bit glib".
Peter's first episode in the role, Deep Breath, is due to kick off series eight of Doctor Who on BBC One on August 23.