Lukas Dhont slept through the Oscars. He was in bed with his boyfriend still recovering from the Césars, France’s answer to the Academy Awards, which had taken place a couple of nights earlier. Girl, his directing debut, had been up for a best foreign film César and there had been predictions that his story of a 15-year old trans girl training to be a ballet dancer and counting the days until gender-confirmation surgery, would be Oscar-nominated too. Which would have been a fairytale ending to a breakthrough year for the 27 year old from Belgium.

In May, Girl premiered to a standing ovation at the Cannes film festival, winning a prize for its 17-year-old male star Victor Polster and three more awards including the Caméra d’Or. Netflix bought the US release and there was a Golden Globe nomination (“the ceremony was surreal, watching Lady Gaga and her amazing lavender dress”). Then came the firestorm.

Girl had already come under attack as yet another example of a trans role being handed to a cis actor. LGBTQ activists also criticised Dhont for fixating on the physical transformation of the central character Lara, who struggles with her body dysphoria and painfully binds her genitals. Then, in December, the trans critic Oliver Whitney wrote a furious essay in the Hollywood Reporter, describing as “sadistic” and “trauma porn” a scene at the end of the film depicting self-harm. Whitney branded Girl “the most dangerous movie about a trans character in years”.

The damage appears to have been done. Girl’s Rotten Tomatoes score has slipped, Netflix delayed the US January launch – it’s now scheduled for 15 March, the same day as its UK cinema release. And in the end, Girl received no love from the Academy. Does Dhont believe this was because of the controversy? He smiles gently. “No. No. I think there were amazing films in the foreign language category. We just didn’t make the cut.”

I meet Dhont in London three days after the Oscars. He looks more like an actor than a film-maker, with tousled hair, cloudy blue-grey eyes, beard trimmed. I’ve interviewed directors defending films before: they tend to be prickly or guns blazing. But Dhont is all smiles. I’ve never met anyone so even-handed about their critics, though he winces when I say “backlash” calling it “such an extreme word”.

How does he feel? Angry? Hurt? “No,” he answers softly in rather formal English. “It doesn’t hurt. For me it’s important to defend the film, but also important hearing people speak who haven’t been allowed to speak enough in the past. For me, Girl is a document to help trans visibility. So we have the same cause, these people criticising the film and me. I don’t want to be against them, I want to be together and pushing forwards.”

He also describes Girl as “a document for Nora”, a reference to Nora Monsecour, the trans dancer who inspired the film. Dhont met her when he was 18 and she was 15, after he read an article about her battle to switch to the girls’ class at ballet school. (To dance as a woman requires en pointe skills, only taught to girls – so to dance professionally she needed to be in that girls’ class.)

Her bravery stopped Dhont in his tracks. At the time he was still in the closet; she helped him come to terms with his identity. “I think I was looking for someone who could pull me over the edge into authenticity. I needed an example of being your true self and she was that to me.” He describes their relationship as “closer than a friendship”.

One of the big criticisms of the film is that it’s told from a cis perspective since neither he nor actor Polster are trans. But Dhont says that Monsecour was with him every step of the way: “She was a constant reader of the scripts. She was on set. She saw the edits.” Back at the start, when they were teenagers, Monsecour told Dhont that she would write her story with him but that she didn’t want her name on the credits.

When Girl came under fire, Monsecour, who dropped classical ballet and is now a modern dancer in Germany, stepped forward to defend – and in a sense claim – the film. Describing it as “my truth”, she has hit out at critics for attempting to silence her and her trans identity. “My story is not a fantasy of the cis director. Lara’s story is my story.” As if to prove the point, twice during our conversation Dhont calls the film’s character Nora instead of Lara.

I ask whether, with the benefit of hindsight, it would have been better to have included Monsecour on the credits? He pulls a face. “For me, of course it would have been easier. Because people would have gone, ‘Oh, a trans woman was here, so now it’s valid.’” But he doesn’t buy the argument that only trans film-makers can make trans films. “Because then you’re saying that you can only speak about that very specific identity that you are.” So he fundamentally believes in his right to tell the story? “Yes. If I did it how I did it, with the respect and love for Nora, where she came from and who she is, then yes I have the right.”

What did it feel like showing her the finished film? Dhont lets out a big sigh and lifts his eyes. It’s the only time during our conversation that his composure slips, and he says softly: “You could have filled a bathtub with tears. It was a moment of catharsis. It was extremely emotional for us.” If she were to appear on the credits, how would he describe her role? “Muse,” he says, then corrects himself. “An active muse. She participated.”

Monsecour was involved in the casting process and gave her blessing to Polster. Her main requirement was actually finding an actor who could dance: “She didn’t mind if the actor wasn’t trans. She wanted someone who would respect her in an elegant way.” Dhont describes the casting as genderless: he auditioned 5oo young people, including trans girls. He has previously said that psychologists at Ghent University Hospital’s Centre for Sexology and Gender (where Monsecour had been a patient) advised against casting a trans girl at a vulnerable point in her transition.

I won’t describe the scene towards the end that’s causing most offence since that would be a spoiler. Monsecour has said the scene is fiction, though it does reflect her dark thoughts at that time. Dhont, too, is convinced he did the right thing by including it. “The film doesn’t hide away from any emotions this character felt – good or bad. And I think the film shows this character a lot of love. So no, I don’t in any way think that it is a harmful film. I think it’s a very loving film.”

The big problem, he says, is that there are simply not enough LGBTQ movies being made. “Girl is the portrait of one person. Because there are so few trans stories, every trans story that arrives, they say, ‘Ah, so this is the trans experience.’ I think it’s a lot about role models. Does every queer character have to be a role model? I think it’s important to stress the fact that this is one young character, one young teenager, one young dancer, one young trans teenager, having a very specific relationship with her body, and not representing every trans experience. I have to repeat that every time. You cannot attack this film for the fact that there are not enough trans films.”

Dhont stands by his work, with absolutely no regrets. Girl has been in his head for nine years, five of them actively working on it. And he’s done his research: working with Monsecour and her family, with transgender charities in Belgium, with parent groups and the Ghent unit. Still, if he had the time again, would he do anything differently? He shakes his head, but it takes him a few moments to gather the words. “No – and that’s not because of stubbornness or self-esteem. It’s because this film was made in a very authentic way with integral …” He stumbles over the word. “How do you say it?”

With integrity? “Yes, with integrity.”

• Girl is released in the UK on 15 March.