Doctor Who revisits old companions in touching scene

"I have this problem," Graham told the group. "See, I met this person and I got whooshed away, across all of space and time. I had the most amazing adventures.

"But I came back and I actually can’t tell anyone, because they’d have me put away – and that started me thinking though… I can’t be the only one."

He certainly isn't – revealed to have accepted Graham's invitation alongside Dan, Yaz, Ace (Sophie Aldred), Tegan (Janet Fielding) and Kate Stewart (Jemma Redgrave) are three classic Doctor Who companions: Melanie Bush (Bonnie Langford), Jo Jones (Katy Manning) and Ian Chesterton (William Russell).

Mel travelled with both the Sixth Doctor (Colin Baker) and the Seventh (Sylvester McCoy) between 1986 and 1987, while Jo – then Jo Grant – was assistant to the Third Doctor (Jon Pertwee) between 1971 and 1973 and last appeared in spin-off The Sarah Jane Adventures in 2010.

Ian, meanwhile, was one of Doctor Who's original cast, debuting in the show's very first episode in 1963 and travelling alongside the First Doctor (William Hartnell) until 1965 – returning to the series almost six decades later, the science teacher gets a mighty surprise...

Reflecting on his own experiences alongside the Doctor, Dan remarks: "I’m glad I’m not on the verge of being exterminated anymore – but I do miss her."

"Sorry… did you say… her?!" says a flabbergasted Ian, learning about regeneration for the first time.

Speaking to press at a screening of the centenary special, Doctor Who showrunner Chris Chibnall said it was essential that the episode be "big", "epic" and "emotional" but also that it have "lots of golden threads back to the past".

"To see William Russell as Ian Chesterton, going right back to the first ever episode of Doctor Who... a lot of people worked very hard to make all of those things happen," Chibnall explained.

"I didn't tell anybody I was going to be doing it – I just put it in the script and sent the script off. I just thought this was the moment when we could ask [those actors to return], and they were all really keen – we just got incredible messages back.

"On the day, it was really emotional, but it was emotional in an amazing way."

Though she wasn't required for filming, Jodie Whittaker revealed that she paid a special visit to the Doctor Who set on the day that the companion reunion was shot. "It was so emotional, it was amazing," she said.

"Walking onto set with people who... this is their show, and you are a tiny drop in the ocean of Doctor Who. For us, we've got to tread lightly and we've got to earn our place. And so then to be on set with people that paved the way for us to be here, it's a really emotional thing.

"I've made no kind of secret of the fact that I'm a relatively new Whovian compared to a lot of people because my introduction into the universe has been getting the job. So to have these kinds of experiences... I know people would kill to be in this position. And so I knew every second of it, you just got to treasure."

Following transmission of The Power of the Doctor, Doctor Who is entering a bold new era for its 60th anniversary and beyond under returning showrunner Russell T Davies. But have we seen the last of these old faces? Perhaps not – after all, Kate did mention she was keen to get them on UNIT's books...

Read more about Doctor Who:

• Doctor Who brings back classic Doctors for centenary special
• Doctor Who revisits old companions in touching scene
• Doctor Who's Sacha Dhawan: 'I'll never, ever forget playing the Master'
• Doctor Who’s Sacha Dhawan “overwhelmed” at getting to play the Doctor
• Sacha Dhawan on his Doctor Who dance sequence: “Yeah, I went for it!”
• Doctor Who’s Sacha Dhawan would “love to come back” to face Ncuti Gatwa

Doctor Who is available to stream on BBC iPlayer with episodes of the classic series also available on BritBox – you can sign up for a 7-day free trial here.

Check out more of our Sci-Fi coverage or visit our TV Guide to see what's on tonight.

The latest issue of Radio Times magazine is on sale now – subscribe now and get the next 12 issues for only £1. or more from the biggest stars in TV, listen to the Radio Times View From My Sofa podcast.