What makes a movie star? Josh O’Connor, the 33-year-old British actor best known until, well, last week as the thin-skinned, tight-lipped Prince Charles in seasons three and four of The Crown, has been mulling over this question of late. Earlier this year he completed a drama set in the first world war called The History of Sound, with Paul Mescal. “Paul’s a friend, and to watch him work was amazing,” says O’Connor. “I really can’t underplay how brilliant he is. Paul has that movie-star quality, whatever that is. I wish I could articulate it, but he’s just graceful about it all.”

Zendaya is another one. O’Connor is currently in cinemas alongside her in Challengers, Luca Guadagnino’s critically acclaimed psychosexual tennis romp, which topped the box offices in both the UK and US last weekend. They play two sides of a lascivious love triangle, with Mike Faist as the third, but it is clear that Zendaya’s Tashi Duncan is the one pulling the strings. “I’ve never done premieres like I’ve done with Challengers,” says O’Connor. “So that’s alien to me anyway, but to see how she breezes through them with such class and generosity. I’m a nervous wreck, I don’t think I’m helpful to anyone. And Mike as well, we’re both a bit like: ‘What the fuck? This is mad!’ But she’s just on the nail.

“Call it what you want: chemistry, alchemy, talent, movie-star quality – Zendaya has it,” he goes on. “She’s just hit the jackpot.”

What about O’Connor: does he have movie-star potential? Or could he? “No!” he replies, with a self-deprecating giggle. “I don’t think I have. That’s not me being faux-humble. I’m too anxious a person. I don’t know that I have those attributes really. I don’t think I’m quite strong enough to be a movie star.”

He might be right, but that’s in no way a criticism. When we meet, on a Monday morning in a hotel bar in Soho, he has just returned from the multi-week, global promotional tour for Challengers. “Which has been exhausting and confusing and scary – like, baffling at times,” says O’Connor, who has tousled brown hair and the patchy beginnings of a beard, leaning back on the mustard-yellow banquette and sipping a cappuccino. “But at the same time, I was in Sydney one week and me and Mike walked over the top of the Sydney Harbour Bridge and it was amazing. Or I was in Monte Carlo. I’d never go to Monte Carlo and I was in this hotel room that I’ve never seen the like of, and I went into a casino. I felt like I was James Bond.”

Did he gamble? “No, I didn’t. Well, that’s the party line.” A beat. “No, I actually didn’t.”

O’Connor has a gentle, solicitous manner: when, later on, he talks about losing out on a job and feeling joy for the other actor who landed it in his place, you actually, just about, believe him. At home, his favoured “side hustles” are making ceramics and gardening. Unable to do these on the press tour, he started doing embroidery. He grabs his phone to show a couple of examples and – I’m not just saying this – they are genuinely impressive. I ask if he might put them on his Instagram, which is mostly images of pots and sculptures and black and white photography, and looks more like the curation of an artist than an actor. He winces; he doesn’t post so much on the site any more, he says. “I’ll just send it to my mum or friends and be like: ‘Look, I did some embroidery!’ That serves the purpose of showing off without having to show it off to the masses.”

All of which is to observe that O’Connor doesn’t radiate classic movie-star vibes. And that’s the case on screen as well. Movie stars tend to be bigger, more charismatic than their characters; they exert a gravitational pull. You never forget, for example, that you are watching Tom Cruise in a Tom Cruise film. O’Connor’s great skill, meanwhile, is to fully disappear into the parts that he plays. You never feel like you are watching Josh O’Connor in a Josh O’Connor film, even when you are.

Francis Lee, who directed O’Connor in his breakthrough 2017 film God’s Own Country, in which he played a repressed Yorkshire farmhand, has compared his transformative skills to those of Daniel Day-Lewis (a rare occasion where that comparison hasn’t looked ludicrous). Peter Morgan, the creator of The Crown, has said that O’Connor’s arrival on the series reminded him of when he first worked with a little-known Michael Sheen on the 2003 Blair-Brown drama The Deal.

O’Connor’s ability to shift shapes has never been more obvious than now. In Challengers, he is totally convincing as Patrick Zweig, a cocksure yet underachieving American tennis player who was at least partly modelled on the fiery Australian pro Nick Kyrgios. But also, from 10 May, O’Connor can be seen as the lead, Arthur, in La Chimera, a new film from the Italian auteur Alice Rohrwacher (director of Happy As Lazzaro) that was a big hit at Cannes last year (and has since amassed high-profile fans including Greta Gerwig, who has said she’s “in love” with Rohrwacher’s work). Arthur is the talisman of a band of tombaroli, Italian grave robbers who rely on his gift for dowsing to find ancient objects buried in Etruscan tombs that they dig up and sell on the black market. It is a magnetic film, rich in magical realism, that sometimes feels more like a wild documentary than a narrative feature.

Certainly the two films, and O’Connor’s roles, could scarcely be more contrasting. That went for the experience of shooting them, too. For Challengers, O’Connor, who by his own admission is not a regular at the gym, had to be toned and muscular. He also had to be passably proficient at tennis (even though doubles are used for many of the action scenes) and had daily sessions for a month with Brad Gilbert, who has coached Andre Agassi and Coco Gauff. Guadagnino, who previously directed Call Me By Your Name, installed the actors in penthouses at the Four Seasons in Boston so they could recover from their efforts at the day’s end.

“Luca once described to me that actors are like racehorses,” says O’Connor, smiling. “And in order for your racehorse to be the best it can be, it has to be groomed and looked after and kept in a nice stable.”

La Chimera, on the other hand, was shot in Italy in two sections: the first half in winter, then a break – during which O’Connor filmed Challengers – then back for the second half in summer. After all that tennis, O’Connor returned to the La Chimera set unprecedentedly ripped: “I got into, like, for me, God form. I’ve never been in that shape in my life.” This made no sense for Arthur in La Chimera who has not long been released from prison and is crushed by the death of his girlfriend. O’Connor went on a crash diet, eating just a tin of tuna and an apple for the day’s main meal.

O’Connor’s original plan was to live in Arthur’s shack on a hillside in Lazio, but this was deemed too primitive by Rohrwacher: it didn’t have a functioning toilet or, indeed, much of a roof or walls. A compromise was struck that O’Connor would stay in his camper van, a refurbished DHL delivery truck that he calls Winnie and has painted sunshine yellow. Every Sunday, he would paddle across Lake Bolsena in a canoe on loan from Rohrwacher to buy his week’s shopping from the local village.

“I’ve noticed when I talk about being in a camper van on the side of a hill, it makes people think, ‘Oh he’s gone method,’” says O’Connor. “But truly it was the best possible accommodation available to me. I was right by Lake Bolsena, it was so beautiful. I had my solar shower, which you leave in the sun and you stick it on the tree. So I had hot showers every day.”

What about looking after your racehorse? “It actually was luxurious,” he corrects me, “and suits me better than the Four Seasons, which is nice but a little soulless.”

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There’s definitely a hippy streak in O’Connor, which he traces back to his childhood. He grew up in Cheltenham, the middle of three boys, to John, an English teacher, and Emily, a midwife, both now retired. Holidays were spent camping in France or walking up mountains. O’Connor didn’t especially enjoy it at the time, but the habit has stuck. “The camper van is very much still present in my life,” he says. “It’s parked at my friend’s farm, but when I next get a chance for a holiday, I’ll be in the van.”

O’Connor grew up surrounded by creative types: his grandfather, John Bunting, was a sculptor who taught Antony Gormley, and his grandmother, Romola Jane Farquharson, a respected ceramicist; his aunt, Madeleine Bunting, wrote books and columns for the Guardian. O’Connor, who has dyslexia, was educated at St Edward’s Cheltenham, a private, co-ed school where his father taught. He excelled at art, but eventually drifted into acting and earned a spot at Bristol Old Vic theatre school, which Daniel Day-Lewis and Pete Postlethwaite, two of his idols, had attended. He recalls lectures on Stanislavski and Meisner, pioneers of acting theory, and “someone else, I can’t remember the name”, as he tried to figure out what his approach would be when the time came.

There wasn’t much opportunity in O’Connor’s early gigs: bit-parts in Doctor Who and Peaky Blinders; a bigger one as Larry in ITV’s The Durrells. But his chance came with God’s Own Country, Francis Lee’s debut film. To prepare for the role, O’Connor spent weeks working on a sheep farm in Yorkshire, building stone walls and delivering lambs. Eventually, he ran himself so ragged, losing more than 10 kilos (22lb) in weight, that he ended up in hospital for a week on a drip.

“That was the closest to method, to a method that I did,” says O’Connor. “And I got very sick, which maybe highlights that. That film will always be very close to my heart and Francis is a huge inspiration. Still now. But it took a lot out of me. And it took me a few years to realise the impact that had had on my mental health and how I was working. And to realise I wouldn’t be able to maintain that level of in-depth living and working long-term – it just wouldn’t work.”

For O’Connor now, there is a distinction between remaining focused and prepared as an actor and closing yourself off to the world. “I basically shut down for that period of making the film,” he says, of God’s Own Country. “It was the beginning of my career, so it was easier to shut down to a point, and it wasn’t such a long shoot. But if I was to do that same method on La Chimera and Challengers, I wouldn’t have seen or spoken to my family and friends for a year, which would have been insane. And so, just from my mental health point of view, it’s not sustainable. I’d be devastated.”

Still, O’Connor understands the pull of a fully immersive performance: he won a British independent film award for best actor for God’s Own Country, and the film was one of the reasons he started speaking to Guadagnino about working together. “And I also think actors like to feel like they’re working,” he says, breaking into a goofy grin. “The idea of suffering for your art is very attractive. And it felt like that on God’s Own Country: it wasn’t nice being in hospital for a week, but I remember at the time thinking: ‘This is the stuff! This is how it goes!’ It’s just nice to feel like you’re working hard, that’s the truth.”

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Mainstream success and more awards – a Golden Globe and an Emmy for best actor in 2021 – followed with The Crown. When he was initially invited to audition for the series, O’Connor declined. “Not because I was reticent about everything around it, it was just that I didn’t fully understand what the pull was to play someone like Charles,” he says. “It was only when I went in and chatted to them that I suddenly realised how much of an opportunity that character was. And I’m so glad I did. One of the best experiences of my career was making that show.”

O’Connor’s read on Charles was an empathetic one: at times naive and underestimated; later, becoming more tetchy and neurotic. The actor had the unsettling experience of going into the Covid lockdowns largely unknown and coming out a name (the fourth season of The Crown, which tracked Charles’s relationship with Lady Diana Spencer, was released on Netflix in November 2020). O’Connor has chatted with Mescal about his similarly discombobulating journey with Normal People, which also came out in that period, although he accepts that the scales were significantly more loaded for his friend. “When lockdown lifted, he was the most photographed man in the world,” says O’Connor. “That must have been a real shock to the system.”

Last year, O’Connor moved from a flat in north London to a house in a village outside Stroud, Gloucestershire. A big part of the appeal was to be close to his family, but mainly he wanted a bigger garden and a small ceramics studio. (He politely declines to say whether he currently has a partner.) This summer, O’Connor’s younger brother is coming to stay and they are going to dig a pond. “I sort of loved London for a bit,” he says. “But I always remember an article in the Guardian that my Auntie Madeleine wrote. Basically there was this line that people move to London to work enough so that they can move out.”

Because of Challengers and La Chimera, O’Connor hasn’t had much time at home recently. But Challengers is out in the world now and is striking a chord: “the horniest movie of the year”, noted New York magazine approvingly. O’Connor is especially pleased to have pulled off a character so removed from his own nature. “That was the scariest bit with Patrick, but it was also the most attractive bit, because I don’t think I’ve done that before,” he says. “To fully enter into that complete arrogance, confidence, wherever you want to call it. When the truth is, I err on the side of solitude and keeping myself to myself and I live in the country, like to be left alone. But Luca is very good at just going: ‘Forget who you are. Let’s focus on the parts of you that could lend themselves to Patrick, and pull those out.’”

Was O’Connor worried about the tennis not looking realistic? “Actors are very good at learning enough of a skill,” he says. “On The Crown, I remember having to learn polo. I did two sessions and I was like: ‘Guys, are you sure that’s enough?’ We are jacks of all trades, masters of none.”

Again, with La Chimera, the emotions are the total opposite: Arthur is probably the most attuned O’Connor has ever felt towards a character. “It’s funny because La Chimera feels like the core of my soul,” he says. “Not only because I gave so much of myself to that role, but also Alice [Rohrwacher] is my hero. She’s like a sister to me and the people involved in that film are like family to me. So it’s my baby, and you want to send it off into to the world.”

Our time is almost up, so I ask O’Connor what lessons he has taken from the past few chaotic months. He replies, tangentially, by bringing up one of his favourite books: Candide, Voltaire’s 1759 satire that set out to destroy the optimism of those times. “This is such an interview move,” laughs O’Connor, “particularly with the Observer, to be like: ‘Let’s drop in some literature, keep everyone happy!’” In particular, O’Connor refers to the ending, where Candide and his companions travel to Turkey and meet an old man sitting under a tree. Impressed by the simple ease with which he lives, they ask for his secret to a happy life. “We must cultivate our garden,” the man responds.

“My reading of that conclusion is that gardening is, at its heart, a small act of life,” says O’Connor. “You tend to this thing, which gives you some joy for, particularly in the UK, like, two months of the year. Then it dies and you tend to it again, you enjoy it, then it dies. It’s repetitive and pointless, but we do it.”

I’m a little confused: what exactly does this have to do with O’Connor’s career? “My response to the past couple of months isn’t: ‘Oh yes please, more of that,’” he explains, patiently. “I love making work, but I also love being in my garden and tending to plants and watching them live and die. That contrast, I’m hoping, will keep me grounded.”

So, Josh O’Connor, maybe not a movie star, but perhaps something even more special. That is, if he can be prised away from his garden.

• La Chimera is in cinemas from 10 May. Challengers is out now