Robert De Niro is a busy man this Cannes. In between giving scary motivational talks to his jury - "Enthusiasms, enthusiasms... What are mine? What is that which gives me joy? Almodóvar? Van Sant? Ramsay?" - he's popped out to sign up for comedy The Big Wedding, the debut feature of Bucket List writer Justin Zackham.

Hitherto known by its working title 'Gently Down The Stream', The Big Wedding plays De Niro opposite Diane Keaton, a pairing of screen giants if ever there was one. They shared a CV highpoint (though obviously not screentime) in The Godfather: Part II, and to a much lesser extent, 1996 weepie Marvin's Room.

The Big Wedding sees them play Don and Ellie Griffin, a long-divorced couple who pretend they're still married for the sake of their adopted son's wedding and, for reasons not entirely clear to us, his biological mum. "The family looks on in amusement as their past, present and future unravel for all to see", runs the synopsis, "trying not to kill each other in the process."

Also starring are Katherine Heigl and Amanda Seyfried. It's co-produced by Zackham's Two Ton Films and Millennium Films with principal photography kicking off in Greenwich, Connecticut in July.