When it comes to a biopic about a fashion legend like Saint Laurent, one could hardly expect three straight males who claim to know nothing about fashion to make it. Yet, the tumultuous love story of Yves Saint Laurent and his partner Pierre Berge that spanned half a century proved captivating enough. "I really wanted to tell a great French story about people who fight for their dreams," the French director Jalil Lespert said during a special screening at BFI in London. "Yves and Pierre’s story is one of the greatest love and creation stories of the past century. I fell in love with [their story]." The film, based on a book by Laurence Benaïm and Pierre Berge’s letters to the late Yves Saint Laurent, took a year and a half to complete. "I think it was quite fast," says Lespert. "I’m shooting fast, and I’m writing fast. I needed to feel this kind of emergency to create." His biopic on the late designer features 25-year-old French discovery Pierre Niney taking the title role and four time César winner Guillaume Galienne as Pierre Berge. The real Pierre Berge, who is still alive, gave his blessing to the film. "I met Pierre [Berge] several times," says Galienne. "The first time I met him was when I was a teenager, as my parents knew him and had friends in common. But I didn’t want to meet him during the shooting, I didn’t want to be influenced by the character he is today. The only thing I felt I owed to the real Berge was not to betray his grief and his love for Yves." For Pierre Niney, the role of Yves Saint Laurent meant five months of preparation. He worked with three different coaches in order to do the actual sketching in the movie, mimic Yves’ physique and learn the process of making a dress. But the thing Niney found most interesting about the designer was his voice. "I had been spending three or four hours a day with Yves’ voice in my iPod for five months," says Niney. "I was really moved by his voice, he had such a special, poetic way of communicating. The words he chose, the tone of his voice revealed to me both his fragility and the strong ideas he had. There was a strong character behind his every sentence." Even though Pierre Niney confessed to have known little about the fashion or the Yves Saint Laurent’s life prior to making the movie, he leapt at the chance to play him. "Jalil invited me to join his project over a beer in a random bar. He said it was going to be a very personal movie. I think we explored an unbelievable link between two human beings in the film. I was so lucky to be challenged to play this legend, a complicated and beautiful person from the moment he was 21. Obviously, I was going to say 'yes'." The director and the lead actors felt it was essential to make justice to the relationship between Yves Saint Laurent and Pierre Berge. "They were a couple that was beyond the cliches and political correctness," says Guillaume Galienne. "I was fond of their freedom. They went beyond everything, beyond [Yves’] illness for the process of creation." "Jalil, Guillaume and I became a real trio on the set, like a small jazz band," says Pierre Niney. "Our rehearsals were like composing music. It kept changing all the time." Lespert altered a number of scenes during the movie, changing the dialogue or even cutting it out completely if he didn’t believe in a scene. The biopic dealt a lot with a darker side of Yves Saint Laurent’s life, including his alcohol and drug addiction. It was something that Lespert could relate to, having gone through the same problem himself. "It all had to be natural and close to life," says Jalil. "The scene where Yves comes home completely drunk and Pierre hits him had a lot of dialogue. I felt it was impossible. When I used to be like that in the mornings, my wife would just slap me, without much talking. So I re-wrote the sequence completely." Yves Saint Laurent took number one spot in the French box office back in January, but received mixed views with critics. "I knew that people would expect a lot of us, but I tried not to think about it," says Lespert. "We just tried to do the job, without taking everything too seriously. It was my interpretation, Pierre’s interpretation and Guillaume’s interpretation of the story." He admitted to having "a feeling one can call a 'stage fright' " during the shooting. The director and the cast’s feelings might be tested again in October this year, when the rivaling biopic Saint Laurent with Gaspard Ulliel and Léa Seydoux opens in France. Meanwhile, their film is being released in the UK on March 21.