Outgoing “Doctor Who” showrunner Steven Moffat paid emotional tribute to the classic sci-fi series in London, saying that he was signing off from the best series in the history of TV.

“Now I’m leaving I’ll say it – it is actually the greatest television show ever made,'” Moffat said Wednesday night to applause from fans and press gathered for a special screening of the upcoming special Christmas episode. “It’s not ‘The Wire,’ it’s not ‘I Claudius’ or the ‘The Office,’ it’s not even ‘Blue Planet.’ It is ‘Doctor Who.’”

Moffat went on to tell the audience that TV greatness could not be measured by ratings, reviews, or even on-screen perfection, but should be gauged by the number of people whose lives had been changed by the program.

“People change their view of the world and what they are capable of because of a silly show about a man who travels around in time and space in a police box. So never mind the reviews, never mind the ratings or any of that,” he said. “Count the scientists, the musicians, the scholars, the writers, the directors, the actors who became what they are because of this show….I do not even know what is in second place, but without doubt, and by that most important measure, ‘Doctor Who’ is the greatest television series ever made.”

Emotions were running high at the IMAX screening of the Christmas special, “Twice Upon a Time,” at London’s Science Museum, as the cast and team talked about the episode, which sees Peter Capaldi bow out as the time lord and Jodi Whittaker step into the role.

“As we got towards the end it did get increasingly tinged with sadness,” said Mark Gatiss, who has written several episodes of the show and starred in three, including the special. “Overall, it was a joyous thing, and everything that is brilliant and beautiful about ‘Doctor Who’ is there in that episode.”

“We were so close to blubbing and ruining the take,” guest star David Bradley (“Game of Thrones”) said of one of the climactic scenes. Pearl Mackie, who plays recurring character Bill Potts, advised viewers to have hankies at the ready.

“Twice Upon a Time” sees Capaldi, the 12th doctor, join forces with an earlier version of himself, from 709 episodes ago, as viewers are told at the start of the new epsiode. Bradley plays the earlier, first-ever Doctor, with both him and Capaldi needing to regenerate. The story is set against a snowy World War I backdrop, with the team encountering mysterious glass aliens who can freeze time.

The episode stars a host of Doctor Who fan favorites, whose identities the BBC is keen to keep under wraps until Dec. 25.

Asked by a fan about the casting of Whittaker, Moffat said it was a question for new showrunner Chris Chibnall but added: “I think it’s obvious with the Master turning into Missy and so on, the idea was building. It became the low-hanging fruit in a way.”

Moffat singled out “Vincent and the Doctor,” “The Day of the Doctor,” and “Robot of Sherwood” as among his favorite episodes.

Capaldi did not attend the London screening, but host Jo Whiley read out a message from him. “I wish Jodi and the new Tardis team all the best for the future and the past and everything in between. I look forward to watching them journey to new and wonderful places.

“For me it’s been an amazing trip. I went to the end of time, I met fantastical creatures, and I blew them up, but now it’s over – time I was off.”