Cotillard, 41, announced her pregnancy in September via Instagram.
The Dark Knight Rises actress and French actor Canet, who was previously married to Diane Kruger from 2001 to 2006, were friends for years before they began dating in 2007. They welcomed son Marcel in May 2011.
Cotillard opened up about motherhood in the August 2012 issue of Vogue. "I've never been more exhausted. But I've never had more energy," she said at the time. "This is the paradox of being happy. That's where it comes from."
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