When it comes to sheer glamour, no other film director could hold a candle to prolific French auteur Francois Ozon; a thesis could be written just on his selection of scarves. It seems entirely appropriate that we are meeting to discuss his latest film – a lush World War I romantic drama called Frantz – on a private terrace at the San Sebastian Film Festival where everyone who passes through the door is immediately pressed to accept a glass of champagne. The sunset is throwing the distant Pyrenean foothills into relief; Ozon considers which language to use. "I think English," he says, his accent the aural equivalent of a chocolate eclair. "I need to practise my Eeng-leesh."
Creating a bridge between cultures is crucially at the heart of Frantz, which is set in the aftermath of "the war to end all wars". It is based on a 1925 play by Maurice Rostand, a writer Ozon says has been largely forgotten; it tells the story of Adrien (Pierre Niney), a French soldier who makes his way after the war to a small German town to lay flowers on the grave of Frantz Hoffmeister, the only son of the local doctor and his wife and the former fiance of grieving Anna (Paula Beer), who sees him in the cemetery when she comes on her own daily visit.
As Frantz had once been a student in Paris, the Hoffmeisters assume that Adrien must have been a friend of their son's before the war began. Gradually, they overcome their initial horror of fraternising with the enemy and take him into their home. Anna immediately warms to him, at first because she believes him to have been close to her beloved Frantz and then because she finds he has awakened in her the desire to live. Perhaps she could be in love with him.
Admittedly, Adrien comes with baggage. He has fits of acute emotional distress – collapsing in a dead faint when Frantz's parents ask him to play their son's violin, for example. His grief for Frantz seems fathomless. But perhaps this was nothing unusual among returned soldiers in 1919.
"It's a period of mourning: more than 11 million young people died in Europe after the First World War, so it was quite normal," Ozon points out. Adrien's distress, however, has other roots. It is only as he prepares to go back to France that he is compelled to tell Anna that he has been spinning her a tissue of lies.
"I thought it was a beautiful story," says Ozon. "Of course I knew I would change and adapt it, if only because it was written before the Second World War." It is impossible now to pretend innocence of what happened next; Ozon accordingly makes the doctor a member of a local patriotic society with some members already looking forward to creating a new and even bloodier kind of German nationalism. Trouble came, however, when he discovered that the masterly German filmmaker Ernst Lubitsch had already adapted the play as Broken Arrows, a declarative pacifist drama very different from his better-known comedies of manners, in 1932.
"When I realised that, I was very disappointed and I thought I will stop everything," says Ozon. "How can I come after Lubitsch? But when I saw the Lubitsch film I realised it was really about the French guy and my idea was to tell the story from the point of view of the losers of the war – and particularly from the point of view of this young girl. So my film would be like a response as a French director."
Lubitsch, who was born in Berlin, told the story from the French point of view; Ozon would adopt the narrative voice of a German. Adrien's confession, moreover, would not be the culmination of the story but its central turning point. The two characters and the two countries become mirrors of each other.
Ozon's filmography is both extensive – he has made a film almost every year since See the Sea in 1997 – and extraordinarily varied. His most popular film remains Eight Women (2002), a camp comedy crammed with all of France's best-loved divas, but his work ranges from the grim portrait of grief in Under the Sand (2000) to a fantasy about a couple giving birth to a winged cherub in Ricky (2009). His films have such a pronounced air of urbane sophistication, however, that it is a surprise to see him gravitate towards an anti-war tract.
"Me too! I never thought that. My first idea was to make a film about secrets and lies," he says. "What I liked in the play when I discovered it was the idea that behind the lie there was a kind of truth. But it also had an important historical background that I decided to research, which was a real challenge as I had never done anything like that. There are so many archives in France about the First World War, so it was quite easy to reconstitute the period. It was much more difficult to recover the Germany of that time, because you realise the Germans have quite forgotten that war."
It was working on location in Quedlingburg in the former East Germany, however, that made him realise he had to shoot most of the film in black and white.
"One day when I was walking around the town I saw some pictures in black and white of the city," he says. "I realised in fact nothing had changed, because the Communist government never had enough money to rebuild. Even so, it was only when you looked at these pictures you felt as if you were in 1919. Because all our memories of this time are in black and white; we have the feeling that the war itself was in black and white. The producers were quite upset, but for me it was a way to make the audience believe in what happens."
Actually, just the idea that he would make a film in Germany is still ruffling some French feathers. "There is a still a strange mentality from the French against the Germans because of the Second World War," he says. His family had friends in Germany and it was the first foreign country he visited as a child. He has been fond of it ever since.
"For me it was a way to pay tribute to the German culture and the German language, which for me is very musical. I wanted to kill the cliches about the language. And the German producers were very happy, because it is the first time a French guy makes a film about them and they are not Nazis."
Frantz is not a parable, but its wistful internationalism certainly strikes a chord in a Europe threatened with disintegration. "Of course I realised making the film that there are resonances with today," says Ozon. "With the rise of nationalism in Europe, with political parties demanding a return to borders and with the fear of migrants."
More than it is about politics, however, Frantz is a romantic melodrama in which the characters are full of silent yearning, constrained by convention.
Ozon is ready for something else now.
"I realised this is a very chaste movie. There is one small kiss," he says. "So the next film will be more sexual. You will have to wait and see. Voila!" He smiles with Gallic mischief in the fading light; we raise our glasses.
Frantz opens on April 13.