Mr. Rousteing saw himself, he said. And that, “being a designer at such a young age, despite the fact fashion gave me my dream, there is a price to pay. You trust less people. And for me, because of being left by what should have been my first love, my mother, that was also hard.”

The film does not have a neat, happy ending, laced-up corset-tight and dripping in diamanté. Though the social worker was able to pass Mr. Rousteing’s file to another office, which searched for and found his birth mother — and learned that she was still in France — it could not legally reveal her name. Instead, he was offered the chance to write a letter that the social workers would deliver to her, giving her the opportunity to decide if she wanted to meet him and reveal herself. Mr. Rousteing, still unsure whether his fear of another rejection outweighs his need to understand that rejection in the first place, has not decided what he will do.

In the meantime, he had been forced to revise his own origin story, and assumptions about himself.

‘You Can Have the Dream’

Mr. Rousteing had always, he said, hoped his birth parents were “two young people who were very in love with each other but couldn’t stay together.” He had always assumed he was of mixed race, because of his skin color. Both ideas were wrong. “She was Somalian and he was Ethiopian, which means I am African-African,” Mr. Rousteing said. “I’m black.” It’s discombobulating discovering, in your 30s, that the myths you told yourself your entire life, even if you knew you had made them up, were all wrong.

But, “I don’t want anyone to have pity for me,” Mr. Rousteing said. “I want people to see this as a movie about a fighter who faced the world. There is a real crisis of identity today, it’s hard to be yourself. But maybe the people who see it will understand me more.”