Zac Efron and Robert De Niro are attached to star in “Driving Dick Kelly,” an adult comedy formerly known as “Dirty Grandpa” that Dan Mazer will direct for Bill Block‘s QED International, TheWrap has learned.

Barry Josephson is producing the project, which was previously set up at Universal and is now being shopped to other studios.

John Phillips wrote the script, which follows a lascivious, recently widowed Army veteran (De Niro) who tricks his uptight grandson (Efron) into escorting him to Florida for spring break.

Jeff Bridges and Michael Douglas were previously rumored to be up for the fun title role that will now be played by two-time Oscar winner De Niro.

...Mazer co-wrote “Borat” and “Bruno” with Sacha Baron Cohen, and he also served as an executive producer on “The Dictator.” He most recently wrote and directed the romantic comedy “I Give It a Year,” which starred Efron's “Neighbors” co-star Rose Byrne.