The `Inception` actress recently toured for two months with her musician friend Yodelice, playing a variety of instruments and singing under the name Simone.
She explained: "I was in Los Angeles last January, a friend called me up who is an amazing singer who goes by the name Yodelice. He said, `Would you come to the studio? I would love for you to sing one of my songs. `So I went down and ended up going from a background singer to being in a duet. Then my friend said he was playing at the Olympia in Paris and asked me if I would sing with him there and I said, `Oh, yeah, of course.`
"I was part of the band, playing all of the instruments. I ended up on tour with Yodelice for two months, travelling around to shows in different cities in France and Belgium.
"I changed my name, of course. I said, `I can`t be MarionCotillard.` We ended up using Simone, which is my other grandmother-s name. She passed away many years ago but always wanted to be a singer. So sometimes Simone appears with the band."
Although Marion - who also experimented with the bass guitar, piano and drums when working with Yodelice - had to stop performing with her pal to complete her filming commitments, she is now looking forward to going on the road as her alter ego again.
She added to Interview magazine: "I love being Simone. I`m waiting for my schedule to open up in a month or two so I can pick up with the band and be a musician again.
"I love being one of the musicians in the back. The light is on the singer and I`m in the band. I love that."