John Simm's favourite 'Doctor Who' experience was playing janitor Mr. Razor on the Cybermen's ship.

Michelle Gomez, John Simm and Peter Capaldi

Michelle Gomez, John Simm and Peter Capaldi

The 50-year-old actor loved playing the evil Master - which he starred as during David Tennant and Matt Smith's stints in the TARDIS before returning towards the end of Peter Capadli's run three years ago - and now he's opened up on his best memory.

Speaking to 'Doctor Who' director Rachel Talalay, he admitted his appearances in 2017's 'World Enough and Time' and 'The Doctor Falls' stand up above the rest.

He said: "My favourite bit, believe it or not, was being Mr. Razor... I adore these two episodes and remain incredibly proud to have been involved in the demise of not one but two Doctors."

In the plot for the episodes, the Master was disguised as Mr. Razor to trap companion Bill Potts (Pearl Mackie) below deck on the ship, forcing his enemy - played by Capaldi - and his own future incarnation Missy (Michelle Gomez) to join him for the big reveal.

The memorable moment marked the end of both John and Michelle's appearances as the Time Lord.

Most recently, Sacha Dhawan took over the role - making his first appearance in 'Spyfall' on New Year's Day (01.01.20).

Back in March, the 35-year-old actor admitted he's had a blast playing the iconic sci-fi villain and he'd be delighted to have a long run on the show.

He said: "Yeah, I'd love to [return]. I'm just waiting to be asked, to be honest. I think, for me, I wasn't like, 'Oh, I hope this is a regular thing!'

"I think the challenge for me was doing the role justice. The response has been really good, and really overwhelming. Hopefully, it'll still continue like that.

"So I'm just happy that the fans like it. And in all honesty, that's enough for me. If they ask me to come back, it's an added bonus."