The Crazy, Stupid, Love actor's first film behind the camera, Lost River, stars Doctor Who actor Matt Smith and Mad Men actress Christina Hendricks.
Also starring Reda Kateb and Marvel's Agent of S.H.I.E.L.D star Ian De Caestecker, the film has been billed as a fantasy thriller. It follows Christina's character, a single mother who is swept into a dark underworld, while her teenage son discovers a road that leads him to a secret underwater town.
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Eva quashed rumours that the pair had split earlier in March when she said of the film: "Ryan really created the most beautiful, collaborative, creative atmosphere on set. I know I'm biased. He's the best, he's the best."
French actress Marion Cotillard was also on the French Riviera on Tuesday for a photocall for her latest film, Two Days One Night.
Wearing a gorgeous couture dress from Maison Martin Margiela, Marion was joined by the Dardenne Brothers, the directors of the film.
The two-time Palme d'Or-winning film-makers look to be possibly heading for their third award following rave reviews from critics.
Also at the annual film festival were Rosie Huntington-Whitely and Elvis Presley's granddaughter Riley Keough.
Rosie looked chic in a pale blue cut-out Victoria Beckham dress as she helped launch Magnum's glamorous new commercial to mark the ice-cream brand's 25th anniversary.
Actress Riley is best friends with Kristen Stewart and expected to join Kristen on the red carpet this Friday as she premieres Sils Maria. She paired a low-cut white blouse with a gorgeous floral A-line midi-skirt from the Valentino Fall 2014 collection as she walked the red carpet for Foxcatcher on Monday.