Katherine Heigl, Amanda Seyfried also star in indie comedy

Robert De Niro, Diane Kea­ton, Katherine Heigl and Amanda Seyfried are set to star in the indie comedy “Gently Down the Stream.”

Justin Zackham (“The Bucket List”) will write and direct the pic, a co-production between the filmmaker’s Two Ton Films banner and Millennium Films.

De Niro and Keaton will play a long-divorced couple who, for the sake of their adopted son’s wedding and his biological mother, pretend they are still married. They quickly learn that acting the part isn’t easy, especially when their past, present and future unravel for all to see.

Zackham and his Two Ton Films partner Clay Pecorin will produce with Richard Salvatore and Harry Ufland, while Avi Lerner, Danny Dimbort and Trevor Short will exec produce. Production is scheduled to start this July in Greenwich, Conn.

Lerner’s Nu Image/Millennium Films will be selling foreign rights to the film, which will be retitled “The Big Wedding” overseas.

“I’m excited to be able to continue what we started with on ‘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,” said Zackham. “Nu Image/Millennium has been a great partner, and I’m honored to have such an amazing cast.”

“Working with Diane and De Niro again will be great,” said Lerner. “Katherine and Amanda are young talented actors. It is good casting. Justin’s script is well written and he is the right choice to direct. It is going to be warm-hearted funny film.”

Other Nu Image titles available at Cannes include “The Expendables 2,” “The Texas Chainsaw Massacre 3D,” “Medallion” and “Playing the Field.”

De Niro and Keaton have worked together twice before, on “The Godfather: Part II” and “Marvin’s Room.”

De Niro and Zackham are repped by CAA, Keaton by WME, Heigl by Paradigm and Seyfried by Innovative Artists.

Follow @Variety on Twitter for breaking news, reviews and more