How Doctor Who used umbrellas, black cloth, lies and codenames to keep Captain Jack Harkness’ return a secret

“Chris [Chibnall] said ‘You cannot say anything,’” Barrowman told RadioTimes.com.

“But I say this because you tell your spouses - the only person that I told was my husband Scott. Well, I tell a fib there - I also told my sister because my sister is also a massive Who fan and Torchwood fan and Jack fan.

“And also we've written the comics together, and a Torchwood novel, and we've done the things together to try and keep Jack out there. So I told my sister and called her also. So there was two people that knew.”

For anyone else, though? Barrowman just lied. And when the time came for him to film his scenes in October 2019, he quickly invented a cover story for why he’d be spending so much time in Cardiff, telling fans he was there redecorating his flat.

“I felt bad but I had to think of something to throw people off the path of what I was doing in Cardiff,” he said, adding that he did end up having to redo the decoration just to make it convincing.

“I'm sitting here right now, in the flat in Cardiff. It's renovated, it's beautiful, and it was a lie at first.”

When it came to filming itself, the production team also followed careful procedures to disguise Barrowman’s involvement, using a codename (an anagram of Billie Piper’s ex-companion Rose Tyler) on scripts and on set and keeping the actor sealed off from the outside world – even when he was in transit.

“They shrouded me in black cloth when I was in the car being driven to Bristol,” Barrowman told us, revealing that Jack’s scenes in the new episode were shot in a different location to Doctor Who’s usual Roath Lock Studios.

“When I got to Bristol and got to the Cathedral to film, they took me out of the car covered in the black, covered me with umbrellas so nobody could see me and put me in the building. And that was me - I had to stay in there all day.”

Unfortunately, the top-secret nature of Barrowman’s scenes meant that he was kept inside the building all day, with no-one willing to risk the chance of anyone spotting them filming. (Retrospectively, this prudence was probably a good move, given that later that same month an apparent scene of Daleks on Bristol’s Clifton Suspension Bridge was photographed by fans on social media.)

“I had just flown in from LA, I was jet-lagged like crazy, and I was there from about eight in the morning until about six or seven in the evening,” Barrowman recalled.

“And it was a long, long day, because we had to do everything in that building, that day.”

Still, in the end Barrowman says it was all worth it to deliver a genuine surprise – and when we spoke to him, he was hoping for a big reaction.

“I always want to build that excitement as much as I possibly can,” he said. “I'm going to try and throw people off the path. But nobody guessed! Nobody had a clue.

He added: “It’s going to be a surprise. Literally people are going to go 'S**t!' right? They're just going to be like 'Oh my God!' People are going to be jumping up and down because it's a reveal, that's all I can say.”

And all it took was some black cloth, umbrellas, anagrams and a few trips to B & Q. Definitely worth it, we’d say.

Doctor Who continues on BBC One at 7:10pm on Sundays