Actor Topher Grace has signed onto the cast of Gently Down the Stream for writer-director Justin Zackham.

The story centers on Robert De Niro and Diane Keaton's characters, a couple who have been divorced for many years, but pretend to be married again for the sake of their adopted son's wedding. Topher Grace will play the biological son of Robert De Niro and Diane Keaton, who gets in a bit of trouble when he falls for a young Latin woman. The Latin woman turns out to be the sister of his adopted brother.

The Bucket List screenwriter Justin Zackham will make his directorial debut with Gently Down the Stream, working from his own original screenplay. Production is scheduled to start in July, with filming to take place in Connecticut.