Reports claimed that the 40-year-old actress (who has been in a long-term relationship with Guillaume Canet) and Pitt had an affair while filming the upcoming World War II romantic thriller, Allied. She has since gone on record to deny those claims.
So just who is Cotillard, and how did this rumor come to be? ET's rounded up five things you need to know!
1. She's pregnant -- but NOT with Pitt's baby!
Less than 24 hours after the world learned of Pitt and Jolie's shocking split, the New York Post reported that Jolie had hired a private eye to follow her husband, after she became suspicious he was cheating on her with Cotillard. The French actress took to Instagram to slam the rumors alleging that she was responsible for their breakup. "This is going to be my first and only reaction to the whirlwind news that broke 24 hours ago and that I was swept into," she wrote. "I am not used to commenting on things like this nor taking them seriously but as this situation is spiraling and affecting people I love, I have to speak up."
"Firstly, many years ago, I met the man of my life, father of our son and of the baby we are expecting," she said of Canet and their 5-year-old son, Marcel. "He is my love, my best friend, the only one that I need. Secondly, to those who have indicated that I am devastated, I am very well, thank you. This crafted conversation isn't distressing. And to all the media and the haters who are quick to pass judgement, I sincerely wish you a swift recovery."
She concluded her post by stating that she hopes Pitt and Jolie "will find peace in this very tumultuous moment."
2. Like Jolie, Cotillard is an Oscar winner.
Aside from their strikingly similar good looks, and the fact that they are both mothers, the two actresses have another thing in common -- they both have wrapped their hands around a golden Academy Award statuette. In 2008, Cotillard won an Oscar for Best Actress for her role as French singer Edith Piaf in La Vie en Rose.
She also won a Golden Globe for that role, adorably telling ET, "The nomination was huge, but this was -- I don't know what to say, but I'm very happy!"
3. She supports her competitors.
That same year, Cotillard was nominated for a SAG Award for Outstanding Performance by a Female Actor in a Leading Role. She was up against Jolie, who was nominated for her portrayal of Mariane Pearl in A Mighty Heart.
"They really gave me the desire to be an actress," Cotillard said of being in the same category as some of her idols. "To be here, to have a nomination amongst these amazing actresses, it is something huge."
4. Her current partner was once married to another celebrity.
Before Cotillard swooped Canet off his feet, the French director was married to Diane Kruger from 2001 to 2006. "For a long time I felt that I was so accomplished. 'Oh I speak three languages, I travel the world, I've seen so many things,'" Kruger later said in an interview with Marie Claire U.K. in 2013. "But when I turned 30 I realized I was an idiot. I don't know s**t about anything. At the end of the day, I'm not bitter. I love men. I want a family myself. I'm not angry with him anymore."
5. She's red carpet royalty.
At the 2008 Academy Awards, Cotillard landed a spot on every Best Dressed list for the stunning, mermaid-like Jean Paul Gaultier couture gown she sported to the star-studded show. The fabulous frock has since become one of the best Oscar dresses of all time.