Ncuti Gatwa and Millie Gibson on their "great chemistry", loving Jon Pertwee and the future of Doctor Who

They both burst out laughing. This is what happens when you let the naughty kids sit together in class. It's their comparison, not mine – established the moment they met in September 2022, at Gibson's test for the part of Ruby Sunday, the foundling heroine whose story is, in Gatwa’s words, "the spine of the series".

The meet-cute went like this: Gibson, teenage regular in Coronation Street with an Inside Soap Award on her mantelpiece, arriving early, killing time in a café, then waiting nervously behind an audition room door painted a threatening shade of red. "I was bricking it," she says, "and then I heard Ncuti’s laugh."

Gatwa, Kigali-born alumnus of Sex Education, already announced as the Fifteenth Doctor, making an instant judgement about the new arrival: "We would have been trouble at school together," he says. "That’s what I thought the moment she walked in. Huge smile. Cheeky twinkle in the eye. The teachers would have had a nightmare with us."

The audition went well, but Gibson left in a state of uncertainty. "We had such great chemistry but then I thought, maybe he’s like that with everyone." She received the good news a month later, at a spray tan salon. She tried not to cry off the vegetable dye.

Then the work began. Learning scripts by showrunner Russell T Davies, Gibson sometimes theorising about the plot before Gatwa had read a word. Climbing the rigging of a goblin galleon. Riding a satsuma-coloured Vespa through Cardiff with Bonnie Langford. Negotiating scenes with spacefaring babies and giant slugs. Rehearsing the waltz and the tango. An intense shoot for former showrunner Steven Moffat’s episode, Boom, in which the Doctor puts his foot on an alien landmine, forcing him to defeat that week’s menace without budging from a sulphurous alien crater constructed in the studio.

"We weren’t seeing daylight," says Gibson. "We had black noses at the end of the day because of the amount of smoke on set." A whole season was finished and the next begun before the Christmas episode had even been transmitted.

"You’re knackered by the end of the day," says Gatwa. "You’ll start with a comedic scene, quickly move on to my best friend has just died in front of my eyes, then afterwards a quick little wildtrack of something that you did yesterday. There isn’t time to be as mischievous as we’d like."

But there was time to build a friendship? "Oh my God, yes," says Gibson. "I spent every single day with this guy for months. We ended up knowing everything about each other."

So do they know each other’s birthdays? "Yes," they chime.

Have they met each other’s families? "Yes."

Do they know each other’s politics? "Absolutely!" says Gatwa.

Enough to know how the other will vote in the next general election? "I’m only just able to vote," says Gibson. Gatwa hoots with laughter, then drops his voice to a sincere whisper. "For you, Millie," he says, "to be 18 and taking on one of the biggest roles in British TV must not have been easy. But you made it look easy. I think people often forget how young you are because of how much you can handle."

The history of Doctor Who might incline them to forget. The TARDIS has whisked many teenagers into space, but only one – 18-year-old Matthew Waterhouse’s doomed boy genius Adric – acted his age. Sophie Aldred was 24 when she won the role of Ace, the baseball-bat wielding 16-year-old who accompanied Sylvester McCoy in the late '80s. When the programme began in 1963, Carole Ann Ford, who played the Doctor's 15-year-old granddaughter Susan, was a married woman with a young child at home. Gibson, though, is only as old as Ruby Sunday.

"I’m so glad I was playing my own age," she says. Then she flashes a wicked look across the table. "Did you know Ncuti couldn’t have a moustache because he was playing a 16-year-old in Sex Education?"

When Gatwa started on Doctor Who, his commitment to the Netflix series had yet to expire. For a short time he shuttled between both sets. "Initially, there was a conversation about keeping me clean shaven for Doctor Who," he says. "But I’d spent the last four years playing a child, at the age of 30, so I said, 'Let me have my moustache back.'" The body cannot grant wishes so briskly, but the make-up department can. "Bella [Arghiros], my make-up artist, would present me with a little bag of pubes every morning," he explains. He doesn’t mean this literally, but he and Gibson are now laughing so much they can barely get the words out. "I went through the process of sticking them on for two months," he says.

"Trimming them," whoops Gibson. "Between every take," adds Gatwa. "As they flap off in the wind. I’m chasing a monster and the director says, 'We’ll have to go again because his moustache is half off.' So when it grew back, I felt very liberated."

Being in a room with this pair is a giddy, chaotic experience. During our conversation, Gatwa tries to guess my star sign. He gets all the way through the zodiac before he gets it right. (We’ve established he’s not psychic.) At another he jumps to his feet and announces that he is bursting for a wee. "I’m younger than you so I can hold it," says Gibson. Bladder control, she says, is crucial to filming Doctor Who. "Especially when you’re in a harness for a good hour."

They show no trace of grandeur. Before our interview, Gatwa had ordered a sly snack between chats – a chicken and mushroom Pot Noodle. Gibson likes telling stories against herself: she booked a January holiday to get away from the UK after the broadcast of the Christmas special. She mimes dodging the paparazzi. "But it’s actually been all right. I think it’s because so many people come up to you in this job and tell you your life is going to change. And I think, when?"

They don’t tell each other everything, however. When Ryan Gosling took to the stage at the Oscars this year to perform Barbie’s showstopper I’m Just Ken, Gibson had no idea that her co-star would be high-kicking in the chorus line in a pink bow tie. "I was sat at home with a loved one of mine and he was the one who pointed it out and said, 'Mills, was that Ncuti on telly?'"

Has Ncuti ever sung that earworm of a song at work? "Every day," sighs Gibson, witheringly. "Every day." Gatwa ignores the mockery. He’s proud, he says, to be a Ken.

Did we know, he asks, that there was a Doctor Who story called The Happiness Patrol (in 1988), in which the TARDIS was painted a shade of Barbie pink? (Oh yes: it’s set in a confectionery-based dystopia where insufficiently cheerful citizens are drowned in strawberry syrup by a state executioner with a strong resemblance to Bertie Bassett.) "Russell says to me, 'How do you know these things from the classic series?' and I say…"

"Because I’m the Doctor and I was there!" interrupts Gibson. "Because I watched them on my research days," he counters. The ruffled dandyism of Jon Pertwee’s Doctor has given him the biggest kick. "I do love a bit of Pertwee," he enthuses. "He’s always got his cha-chas out."

The series has given its new stars a chance to do the same. The Devil’s Chord, featuring the Beatles and a musical supervillain played by drag star Jinkx Monsoon, puts Gatwa in an Afro and blue pinstripe and Gibson in a miniskirt and towering beehive. “We felt the hottest we’ve ever felt in our entire lives,” says Gibson.

"We were so hot," they say, simultaneously.

"I miss looking like that," says Gibson. "So much," says Gatwa.

And here the past tense creeps in. For a long while, rumours have swirled that Gibson’s Ruby Sunday is on her way out already, giving way to a new companion played by Andor actor Varada Sethu for the next season (currently filming to air next year). Now, the BBC have announced Gibson and Sethu will both appear in the 2025 season alongside Gatwa. Either way, Gibson says she hasn’t filmed Ruby’s final scene yet – her day is not yet over.

"I know how it ends next season," she says. "But after that I can only guess. I might be here with a walking stick in a few decades."

60 years of Doctor Who have produced TARDIS crews of varying degrees of intimacy. In the late 1980s, Sylvester McCoy and Sophie Aldred went clubbing after filming. Frazer Hines, who spent three years in the '60s gadding about in a kilt beside Patrick Troughton’s Doctor, also accompanied him as he delivered housekeeping money to his dependents. (Troughton maintained two families whose existence was unknown to each other.)

Tom Baker’s tempestuous romance with Lalla Ward, who played Time Lady Romana, divided rehearsal rooms into opposing camps in the early '80s and is sometimes legible on screen: whole episodes go by without them making eye contact. These new successors, however, can finish each other’s sentences. Sometimes they even speak in unison.

"You get in sync," says Gatwa.

"We Bluetooth emotions," says Gibson, in pure Gen Z. "There’s a lot of eye contact," says Gatwa. And a bit more, right now, behind the desk.

Doctor Who launches with two episodes on BBC iPlayer at midnight on Friday 10 May, followed by a broadcast of both on BBC1 on Saturday 11 May.

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