When people ask Charlotte Wells how she got into filmmaking, sometimes she tells them it was a childhood ambition and sometimes she doesn’t. It’s a question the Edinburgh-raised, New York-based director has been fielding a lot since her debut feature Aftersun became the break-out film of this year’s Cannes Film Festival.

“Sometimes I’ll say when I was a kid I had this idea of being a film director and it just took me a long time to come back round to it,” says Wells over a Zoom call from her apartment in New York. “But that story feels a little bit different knowing I’m coming back to Edinburgh.”

She’s referring to the film’s imminent UK premiere as the opening night gala of this year’s Edinburgh International Film Festival. “Because Edinburgh was the place where I stood up in English class and gave a two-minute talk about wanting to be a film director, it feels more specific. I’m reminded of how important that was to me when I was younger.”

Back then she didn’t really know what a director did; she just lived at the multiplex in Fountainbridge, making the most of her subscription card to see everything coming out and, in her later teen years, spending all her money attending the Film Festival. “I loved films and it was definitely something on my mind. And then, I dunno, it wasn’t something that seemed all that accessible or realistic for a long time.”

Instead she went to university in London, studied classics, did some other jobs, and eventually started finding her way back to that initial passion: first with a job helping an old school friend run his film crew agency in London, then by applying to film school at New York University. Even after getting in – “Not that I thought I would” – she figured she’d end up working on the business side of film production. But after making her first short film as part of her degree course – 2015’s Edinburgh-set Tuesday – she realised what she should be doing and got enough encouragement from her professors, among them American indie film luminaries Kasi Lemmons, Alexandre Rockwell and Todd Solondz, to keep going. “That’s all you need to hear at the beginning,” she says. “I remember being in Todd’s class with the very first draft of that script. He said, ‘There’s something here.’ That was all I needed.”

Cut to seven years later and Aftersun is already one of the most rapturously received British debuts in recent memory, emerging from Critics Week in Cannes with five-star reviews hanging off it like prize tomatoes and Moonlight director Barry Jenkins on board as one of its producers. The acclaim isn’t misplaced either.

Aftersun revolves around a divorced father (rising star Paul Mescal) and his daughter Sophie (newcomer Frankie Corio) as they take a cheap and cheerful package holiday to Turkey. Nothing especially dramatic happens, and yet Wells manages to simultaneously transform this simple story into a vibrant, in-the-moment portrait of the complexities of childhood and fatherhood, and a more abstract meditation on memory.

Aftersun, the debut feature from Edinburgh-born director Charlotte Wells, starring Paul Mescal and Frankie Corio, will open this year's Edinburgh International Film Festival.

“It began by flipping through old photo albums,” says Wells, picking up the story of the film’s origins. “I’d go on holiday with my dad when I was a kid. He was fairly young when I was born and I think just looking back at those pictures with the perspective of being closer to his age was impactful.”

Initially the story was more plot-heavy, with more conflict between the leads. But over time she began drawing on holidays with her dad and childhood experiences with her mum and other family members to create a relaxed, largely joyful portrait of a dad and his daughter, albeit with an undercurrent of melancholy that almost imperceptibly pulls us towards a rawer, more heart-wrenching finale. Don’t be surprised if you leave the cinema bawling your eyes out.

“Yeah, it does seem to be eliciting a strong reaction,” says Wells, who’s been describing it as “emotionally autobiographical” since Cannes.

“I didn’t go on this holiday, but there’s a lot of me in it,” she clarifies, which seems like an appropriate way to describe a film that accrues a lot of its power from what’s not said.

Part of the film’s success in this respect is down to her artful, sophisticated use of flashback to subtly frame the story as the adult Sophie’s reflections on a once-blissful memory that’s become a key to understanding her dad and herself. How did she arrive at this approach?

“With much effort,” she quips. “I never really wanted there to be a very firm, separate timeline, or voiceover. And without those things it was really tricky to show how this perspective of Sophie as an adult was coming through without showing it very much.”

The other big reason the film works is the nuanced portrayal of that central father-daughter relationship. If the film provides another great showcase for Mescal after his breakthrough in TV’s Normal People, the real discovery is Livingston school girl Frankie Corio, who was found after the film’s casting directors put out calls across schools, sports clubs and WhatsApp groups. “We spent about six months casting Sophie,” says Wells. “We ended up having submissions from about 800 kids and then eventually we had 16 kids in person in Glasgow and worked with them over a couple of days. And Frankie just really surprised us.”

Though she’d never acted before, Wells was impressed by her ability to inhabit the character, but also leave her behind when a scene was over. “That just reflected an ability to act. I thought we’d find a kid who already was like Sophie, but instead Frankie was able to become Sophie in her performance.”

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“Frankie is so special,” she adds, beaming. “I can't wait for the Edinburgh screening. We're both going to have a lot of friends and family there. It'll be fun.”

Aftersun opens the Edinburgh International Film Festival on 12 August. For more information, or to book tickets, see www.edfilmfest.org.uk Aftersun is in cinemas nationwide from 19 August

Charlotte Wells on her Edinburgh Film Festival opener Aftersun: 'There's a lot of me in it'