How have we only heard of this now? In a frankly hilarious sounding flick, Zac Efron will star opposite Robert De Niro in the road trip comedy, Dirty Grandpa.

Now that sounds like a sequel to hit Johnny Knoxville comedy Bad Grandpa from last year, but alas this is an entirely different production all together. In the flick De Niro will play Efron's grandfather, a perverted former Army man who thinks his grandson is marrying the wrong woman. They clash on the way to spring break, but, we're sure learn a valuable lesson by the end.

Providing this is filthy and not a safe PG13 this could actually be very funny. De Niro and Efron have both proven to be excellent in overtly comedic roles; the former in countless films, the latter in the smash hit Bad Neighbours.

Dan Mazar, who directed the sporadically OK 'I Give it a Year' is helming. He also regularly works with Sacha Baron Cohen. So don't write him off yet.

Wonder what De Niro thought of Efron's impression of him in Bad Neighbours...