A source tells PEOPLE, however, that the pair’s breakup has nothing to do with Cotillard, who is starring with Pitt in the upcoming World War II drama Allied.
Jolie, 41, filed for divorce Monday, citing irreconcilable differences and stating that she and Pitt, 52, have been separated since last Thursday.
The dramatic decision – after just two years of marriage – follows Jolie’s hiring of “a private eye,” reported the New York Post.
“She felt that he was fooling around with [Cotillard] on the set, and it turns out, he was. And that was the final straw,” a source told the Post in comments PEOPLE’s source disputes.
In Allied, out Nov. 23, Pitt and Cotillard, 40, play undercover allies who begin to develop a romantic relationship as they plan a high-profile assassination.
WATCH: Angelina Jolie Files for Divorce From Brad Pitt
Pitt’s character is a British intelligence officer, and Cotillard’s a French Resistance fighter who poses as his wife.
Of the film – which was inspired by real wartime stories – producer Graham King told PEOPLE, “Brad and Marion immediately had the utmost respect for each other, so once they delved into their characters, their chemistry was electric.”
King said the pair “spent a lot of time developing their characters” with each other and director Robert Zemeckis before filming began.
Pitt and Jolie famously met on the set for their 2005 thriller Mr. & Mrs. Smith. They were married in 2014 – two years after getting engaged. The pair share six children.