Marion Cotillard has "never been more exhausted" since becoming a first-time mother.

'The Dark Knight Rises' actress admitted that she has struggled to find a balance between work and motherhood, after giving birth to son Marcel last year (20.05.12).

She said: "I've never been more exhausted. But I've never had more energy. This is the paradox of being happy. That's where it comes from."

The star plays Wayne Enterprises executive Miranda Tate in the upcoming Christopher Nolan-directed movie.

He said he believed in the French actress - who also appeared in his 2010 motion picture 'Inception' - so much that he restructured the film's $250 million production schedule around her due date.

The 36-year-old Oscar winner's one-year-old child is fathered by 39-year-old actor boyfriend, Guillaume Canet.

He told the August issue of American Vogue: "The word challenging is thrown around as some kind of pejorative to mean an actor who's difficult.

The 41-year-old film professional added: "But Marion is challenging in the true sense of the word. She's so good you don't want to waste that talent. You want to hold up your end."