Steven Moffat has teased the 'Doctor Who' festive special will be "dark and sinister".
The 55-year-old departing show runner - who will hand over the reins to Chris Chibnall at the end of the year - has promised fans that the forthcoming episode, which will air on Christmas Day (25.12.17), will be different from previous years and won't be as tear-jerking and joyous as some people may expect considering it'll be the last time viewers see Peter Capaldi as the time-travelling alien.
When asked how he and 'Sherlock' co-creator Mark Gatiss have balanced the detective's selfish tendencies with his good nature, Moffat spoke about the Doctor in comparison to reluctant hero and told press at the London Screenwriters' Festival: "Why would Superman be good? Because kindness stops you being lonely, would be the answer. That's what that's about, for Sherlock Holmes. He's good because for all he protests about it, there are people he cares about. So, kindness is what makes a unit of us. So if you are sane and rational, kindness is by far the best path. There isn't anything rational about being vile and awful and evil. It's not actually a good strategy.
"Prepare for that to be contradicted on 'Doctor Who' on Christmas Day..."
But, although Moffat has given fans the stark warning, Peter recently teased that his last scene in which his alter-ego regenerates into the new Time Lord (Jodie Whittaker), will be emotional because of the way the screenwriter has written it.
He said recently: "I felt Steven [Moffat] had written something very beautiful, and very right for my Doctor, so I was just happy to try and do my best with it."
Meanwhile, Moffat - who has worked as executive producer on the show since 2009 - recently revealed he saved the festive episode from getting the chop after he learnt that bosses were toying with the idea of taking it off the agenda this year because Chibnall wanted to start in January with series 11 rather than pick up in 2017.
The talented writer was concerned that the festive special would never make it back on screen if they temporarily pulled the plug on it this year and, although he was willing to step in, he had to persuade Peter to continue for a few more months.