Robert De Niro and Diane Keaton have been set to star in the comedy project Gently Down the Stream. Amanda Seyfried and Katherine Heigl have also joined the cast in supporting roles.

The story centers around Robert De Niro and Diane Keaton's characters, a couple who have long since divorced but agree to pretend to be married again, for their adopted son's wedding. It isn't known what roles Amanda Seyfried and Katherine Heigl will have in the comedy.

The Bucket List screenwriter Justin Zackham will make his directorial debut with Gently Down the Stream, working from his own original script. Here's what he had to say about this new project.

"I'm excited to be able to continue what we started with The Bucket List - iconic actors in a funny, adult, character-driven story, albeit with a little more sex and bad behavior on everyone's part. Nu Image/Millenium has been a great partner and I'm honored to have such an amazing cast."

Production is scheduled to start on Gently Down the Stream in July, on location in Grenwich, Connecticut.