The actress rumored to be at the centre of Angelina Jolie and Brad Pitt's divorce has confirmed she is pregnant.
But the 40-year-old denied having an affair with Brad Pitt, after reports of cheating emerged amid the actor's shock split from Jolie.
The French star wrote a lengthy Instagram message to make the announcement and to dispel rumours on Wednesday.
She said: 'This is going to be my first and only reaction to the whirlwind news that broke 24 hours ago and that I was swept up into.
'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.
She went on to confirm that her partner of eight years Guillaume Canet is the father of her unborn child.
'Firstly, many years ago, I met the man of my life, father of our son and of the baby we are expecting. 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 judgment, I sincerely wish you a swift recovery.'
She concluded her message by wishing Brad and Angelina Jolie well.
'Finally, I do very much wish that Angelina and Brad, both whom I deeply respect, will find peace in this very tumultuous moment. With all my love, Marion'.
Cotillard's post comes after she was said to have been left ‘absolutely devastated’ by reports claiming there was more than onscreen chemistry between her and Brad, 52, while filming their movie, Allied.
According to French magazine Closer, she is due to give birth in December.
If correct, the timings would mean she would likely have conceived in March, at a time when she was filming with Brad, although there is nothing to suggest Brad is involved.
She has been in a relationship with actor and director Canet, 43, for almost a decade and they are parents to five-year-old son Marcel.
Agency X17 reported Angelina was crippled by jealousy at the close bond her husband and Marion developed while filming together.
A source said: 'Angie couldn't handle Brad's sex scenes with Marion. Her jealousy was out of control.
'Brad tried for months to reassure her and calm her anxiety, but it simply didn't work. She said her intuition was telling her he was cheating.
'Angie has struggled with insecurity over Brad's fidelity for years, but she was never as jealous over a co-star as she was with Marion.
‘She was always paranoid Brad would do to her the same thing he did to Jen.'
On Tuesday a new trailer for Allied was unveiled, just hours after news of the couple’s divorce broke.
The one minute clip features the actor in a raunchy scene with Marion.
In the movie the pair play an 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 echo Angelina’s own love story with Brad.
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.
They married on August 23, 2014 and have six children together, three of which are adopted.
Oscar-winning Marion was born in Paris, and grew up just south of the French capital in Orleans.
The French beauty dated French singer Mathieu Blanc-Francard for two years up until 2007, when she started seeing Canet.
Their son Marcel was born on May 19th 2011.