Marion Cotillard is said to "absolutely devastated" by claims that she is the scarlet woman in the break up of Brad Pitt and Angelina Jolie.
The 40-year-old French star is in a relationship with fellow actor Guillaume Canet, 43.
"Marion and Guillaume are blissfully happy, and these kind of claims are not what Marion wants to be hearing," a source close to Marion's family in her home city of Paris told Daily Mail.com.
"Claims that she's cheating on Guillaume with Brad will leave her absolutely devastated. This doesn't sound like her at all."
DailyMail.com sought comment from all parties but did not receive a immediate response.
Cotillard gave birth to Marcel, five, while still working extremely hard at her career, but she has recently indicated that she wants a "quieter life", said the source.
"She enjoys her family time and wants to enjoy more of it,' said the source. 'All this fuss will be a huge shock to her."
Cotillard stars alongside Pitt in the upcoming spy thriller Allied and their onscreen sexual chemistry has been described as "electric".
According to the film's producer, Graham King, Pitt and Cotillard had an immediate connection.
"Brad and Marion immediately had the utmost respect for each other, so once they delved into their characters, their chemistry was electric," he told People Magazine back in August.
"It was crucial for Brad and Marion to not only begin rehearsing together before the shoot, but they also spent a lot of time developing their characters with the director, Robert Zemeckis," he added.
"By the time we got to set, it was really amazing to see these characters already feel lived-in and real."
The pair play a information officer and French Resistance fighter who fall in love. They began filming the movie in England in February this year and also travelled to Casablanca and the Canary Islands for shoots.
The shock allegations of an affair, reported by Page Six, are reminiscent of Angelina and Brad's own love story; they met and 'fell in love' on the set of the 2005 spy film Mr and Mrs Smith while he was still married to Jennifer Aniston.
Cotillard, who turns 41 at the end of this month, has been hugely busy working on up four films this year, but has indicated in interviews that she wants to cut down on her frantic pace.
Oscar-winning Cotillard is one of the most successful actresses in recent French movie history, and has built up a multi-million pounds fortune.
Her greatest triumph to date was best actress Academy Award for her portrayal of French cabaret singer Edith Piaf in the 2007 film La Vie en Rose.
It meant Cotillard became the second actress to win an acting Oscar performing in a language other than English.
Cotillard was born in Paris, and grew up just south of the French capital in Orleans.
Her first big showbiz relationship was with Julien Rassam, another actor, and between 2000 and 2005 she was Stephan Guerin-Tillie, another thespian who also works as a director.
Marion dated French singer Mathieu Blanc-Francard for two years up until 2007, when she started seeing Guillaume Canet.
The couple have never married, and Cotillard takes pride in calling Guillaume "my boyfriend". Marcel was born on May 19th 2011.
While Canet is relatively well know in France for his acting, directing and screenwriting, he has never been anything like as successful as Cotillard.
Still, they are often seen as France's answer to Brangelina in their home nation.
Marion has often described herself as someone who has never truly feeling like she fits in, telling The Guardian: 'I couldn't identify with anyone. At school I was considered very strange. I didn't understand the relationships between people.'
She also dedicated herself to her roles - so much so she had to get an exorcism once - but since having her child has changed her ways.