The news last week that John Simm’s Master will be returning to Doctor Who alongside his successor Michelle Gomez was met with a huge amount of excitement from fans – even if the assumption was that it would be a relatively brief cameo. After all, how could it have remained such a well kept secret if there had been anything other than a minimal amount of filming on a closed set?

Well, the answer to that turns out to be surprisingly simple – kind people and a bit of luck – and it also poses the very real possibility that we will be seeing a lot more of the maniacal blond Time Lord than we had first expected.

“We kept it a secret because people in Cardiff are very kind,” the series’ executive producer Brian Minchin told RadioTimes.com exclusively at the BFI & Radio Times festival this weekend.

“He was there for quite a few weeks, he was actually filming on the streets and nobody saw him, and he was in the studio.”

That sounds like a pretty substantial appearance to us. Maybe not multiple episodes, but at the very least a good chunk of one story.

According to Minchin, the interplay between Simm and Gomez is “superb”.

“We were so thrilled by the idea of it, we were delighted,” Minchin told us. “Because John loves Doctor Who, and he loves the whole world of it, so when he heard what [showrunner Steven Moffat] is planning, which I won’t tell you, but when John heard what Steven was planning he was so excited.

“It was brilliant to have him on set – he’s a real joy to have around.”

And it seems the Doctor Who team aren’t too disappointed that the news about Simm leaked out early, despite having originally intended to keep the details under wraps for a while longer.

“When people heard John Simm was back they were excited and they were happy, so I’d be a bit churlish to be complaining about that,” Minchin said.

“And one of the things about Doctor Who is we’re a show people like to find out news about, and that they like to get excited about, and that’s a good thing really. It’d be a bit mean-spirited to whinge about that.

“If you think you know the spoilers of Doctor Who series 10 you’re wrong,” he added. “There’s loads more to come.

“The story of Bill and Peter is going to take some very surprising turns, things are gonna happen to the Doctor that have never happened to him before, and Matt Lucas is going to surprise you as well in his character, what you see from him. And we’re building to the most amazing finale ever!”

Doctor Who returns to BBC1 on Saturday 15th April at 7:20pm