When Meg Bellamy got the call that would change her life — the one telling her that after months of auditions, it was she, among thousands of hopefuls, who would play Kate Middleton in the final season of “The Crown” — she was already standing in the shadow of Windsor Castle. But she wasn’t looking the part of a royal just yet.“I was crouched in costume among the bin lorries of a delivery car park at Legoland,” Ms. Bellamy, 21, said at a London hotel suite last month. “Until that point, my most regular acting gig had been playing a red plastic brick.”In 2022, and with no professional acting experience, she was working as a performer at the theme park when she spotted a casting call on Twitter for the role of Kate Middleton. Competition to play one of the most famous women in the world during her college years was fierce. Thousands of young actresses were posting videos about their auditions. But after a neighbor remarked on her resemblance to Britain’s future queen, Ms. Bellamy, crushed after several drama school rejections schools, decided to try out for the part. Three weeks after sending a tape, she got a call — the first in what would be a several monthslong casting process.“I never really believed I would get the role, not in the beginning anyway,” she said. “But then with every round, I started to feel like I had a real chance, and that it might actually be mine to keep. When it was, I was completely shellshocked.”Now, more than two years after that call, Ms. Bellamy’s trajectory from obscurity to the brink of stardom appears to be well underway. Last week, she appeared on the front of The Daily Telegraph, which used a still from the series that recreated the moment in 2002 when Ms. Middleton, on a charity fashion catwalk in a daringly sheer dress, was rumored to have first turned the head of Prince William.This week, ahead of the release of Part 2 of “The Crown” on Dec. 14, Ms. Bellamy was on the red carpet at the London premiere in a creamy Valentino column gown — 24 hours after attending the Fashion Awards, where she wore a blazer dress with a suit and tie by Huishan Zhang.And for months she has been courted by big fashion names like Gucci and Dior — she attended Dior shows in Paris in July and September — which have a habit of snapping up emerging talent with juicy contracts before they ascend to heights of celebrity. After all, if a fashion house can’t hire the Princess of Wales to sell lipstick and handbags, perhaps the unknown actress playing her to an audience of millions is the next best thing.Ms. Bellamy at a finale celebration of “The Crown” in London this month. “Until last month I’d never been to Hollywood,” she said. “Then I was not just there, but on a red carpet with people shouting my name.”Lia Toby/Getty ImagesMs. Bellamy at the annual Fashion Awards in London in December.Dominic Lipinski/Getty ImagesShe attended the Los Angeles premiere in November.Michael Tran/Agence France-Presse — Getty ImagesOver its six seasons, the casting of “The Crown” has largely been anchored by a constellation of established performers, though it has also boosted the sparkly careers of several new faces, including Emma Corrin, who played Princess Diana in Season 4. What was it about Ms. Bellamy that prompted executives to take a chance on her for this role?“We found that there was an openness to her, an intelligence and a sweetness to her, and a chemistry between her and Ed McVey, who plays Prince William,” said Robert Sterne, the casting director for “The Crown.” “You wanted to go on the journey with Meg. You wanted her to tell you the story.”Doing Kate JusticeMuch has already been made of the parallels between Ms. Bellamy and Ms. Middleton, beyond their delicate features and masses of glossy auburn hair. How both were raised by close families in the royal county of Berkshire. (Ms. Bellamy was actually born in Leeds, in Yorkshire, and has a light Northern twinge that still lingers on some of her vowels.) How both were extremely sporty at school, with a particular love of lacrosse. (Ms. Bellamy, who said she was academic, was also head girl, which is similar to a class president.)But unlike the Princess of Wales, who studied art history at the University of St. Andrews, Ms. Bellamy didn’t attend university. After a number of star turns in school musical productions, including Sandy in “Grease” and Scaramouche in “We Will Rock You,” she wanted only to act. She is acutely aware that people wait a lifetime for a break like hers, which came months after leaving high school.Before the six month shoot, Ms. Bellamy spent months preparing to play Ms. Middleton. She watched documentaries and read newspaper clips compiled by researchers. She also worked with movement and voice coaches to perfect her performance. She took home costumes — a nostalgic Noughties-inspired wardrobe of low-rise flared jeans, peplum tops, chunky belts and fringed suede knee-high boots — to wear as she practiced her lines.Ms. Bellamy as Kate Middleton and Ed McVey, who plays Prince William, in a scene from “The Crown.” Netflix/The Crown“I must have looked insane,” Ms. Bellamy said. “I would be dressed as her, reading a book about her and trying to sound like her while walking around the house.” She noted that while there is endless footage of Ms. Middleton after she formally joined the royal family in 2011, there is little — beyond a handful of paparazzi photographs — from her time at St. Andrews, where she first befriended and then fell in love with Prince William.“Her first press interview was when she became engaged at 29, so she was something of a blank canvas,” Ms. Bellamy said. “I spent a lot of time thinking about what she would have been like before she knew where life would take her and that William would become her husband. I hope that I’ve done Kate justice.”At the same time, she added, it was nice to remove the layer of complexities that come with being a royal and just play her as a girl who’s going to university and falling in love.When photographs of Ms. Bellamy and Mr. McVey filming at St. Andrews emerged this spring — and ever since then — there was intense online interest in her private life and next career steps. (So far, Ms. Bellamy has yet to announce her next role.) Lately she has been working with the stylist Felicity Kay to hone her public image and build a brand for herself.Has being thrust into the spotlight given her a vague notion of what it must be like to be a royal?“It’s something I’ve been thinking about, especially as we’ve done more press ahead of the release,” she said. “I really can’t imagine the level of pressure royals face day to day. I mean, until last month I’d never been to Hollywood. Then I was not just there, but on a red carpet with people shouting my name.”She added: “But I keep telling myself that this is something I’ve always dreamed about. You have to remember that, before all of this, I wore a school uniform and could only afford high-street brands like Primark.” More