'The Immigrant' director James Gray didn't know who his lead actress Marion Cotillard was.

The actress plays a Polish immigrant who moves to New York City in the 1920s in the director's new film - which will receive its world premiere at Cannes Film Festival - but he admits he had no idea he was in the presence of an Oscar winner when they first met.

Speaking at Cannes, he told The Hollywood Reporter: ''I had never seen anything she'd been in. She is the life partner of Guillaume Canet, who wanted me to help translate dialogue for this movie 'Blood Ties', which is showing in Cannes ironically enough.

''We would go out to dinner, and so I met her, and I thought she has such an amazing face. My wife said, 'You don't know who that is? She's an actor, she's won an Oscar.' I know it seems unlikely, but when you have young children, you really never go to the movies. We have a seven, five and three-year-old. But I loved her face and I loved her attitude because she was quiet, but she had a total feistiness that somehow came through anyway. And her whole role is conceived as someone who says very little, but somehow conveys will.''

The French beauty earned a Best Actress Oscar for her role in 'La Vie En Rose' and has since starred in a string of Hollywood films, such as last year's superhero blockbuster 'The Dark Knight Rises'.

'The Immigrant' reunites Gray with regular collaborator Joaquin Phoenix and also stars Jeremy Renner.