British actress Lucy Gordon 'sparkles' as Serge Gainsbourg's muse Jane Birkin

Gordon battled with more than 500 other young actors to play the coltish 1960s English actress and, according to critics, was perfect for the role.

But just weeks after she had finished filming Gainsbourg: Je T'aime, Moi Non Plus, in May last year, she hung herself in the Paris apartment she shared with her cinematographer boyfriend.

Friends said the former Oxford High School pupil had been deeply affected by the suicide of a friend in England.

According to director Joann Sfar, the waste of her talent will be highlighted this Wednesday as the film goes on general release in France. He said that the film owed a considerable amount to Gordon's "generosity, gentleness and immense talent".

"The princess of our fairytale is no longer here," he wrote in tribute. "I feel useless and weak, inventing fictions which are more joyful than the world … I think about Lucy all the time. I am not the only one. This film is for her."

Until the latest film, Gordon's acting career had consisted mainly of smaller parts in films such as Spider-Man 3 and Cédric Klapisch's The Russian Dolls. She also had a central role in a new French comedy, Cineman, which was released in October last year.

Sfar said it was immediately clear to him that she was perfect for the part of Birkin, who is perhaps best known for her raunchy duet with Gainsbourg of the same title as the film.

"We had auditioned more than 500 young actors to play Jane Birkin. All English. None of them were right," wrote Sfar, who is also new to films, having previously worked as a comic strip writer.

"I had even written to Keira Knightley, who never replied. No one had the natural manner, the joy and intelligence of Birkin. Then Lucy wrote to me."

Having been offered the part, Gordon plucked up the courage to visit Birkin, who remained in France after her separation from Gainsbourg in 1980.

"There was such honesty, such freshness in her face that I could not have been more flattered," Birkin told Le Nouvel Observateur last week. "She left as she had come. With great modesty. She had grace. When I heard of her death I couldn't believe it was true."

The film has generated huge excitement in France, where the chain-smoking Gainsbourg is seen as a mythical figure.

It features all of his love affairs, from Elisabeth Levitzky, his first wife with whom he is shown romping on Salvador Dalí's bed, to Françoise-Antoinette "Béatrice" Pancrazzi, with whom he had two children.

As his career took off, he had a short-lived, whirlwind romance with Brigitte Bardot, played in the film by Laetitia Casta.

But it is Gordon's Birkin who is most luminous in the film.

Sfar said the actress had "sparkled" as Gainsbourg's great love and mother of his daughter, the actress and singer Charlotte.

"I remember filming with her outside at night until five o'clock in the morning, when it was cold and wet," he wrote. "She pretended she wasn't cold. And she smiled all the time."