Zac Efron and Robert De Niro go shirtless and party hard in 'Dirty Grandpa' trailer

It's a pairing you never thought could ever happen, until it did: Zac Efron and Robert De Niro are starring in a spring break comedy. 

It's called "$4."

In it, Efron plays an uptight guy who is about to get married to Julianne Hough, but not before his perverted retired Army General grandfather (De Niro) has him let loose in Daytona Beach, Florida, for some sunny and shirtless spring partying with the old man.

"Dirty Grandpa" opens January 22 and also stars Aubrey Plaza as a fellow spring breaker who has the hots for De Niro. Yes, you read that correctly.

Watch the trailer, released exclusively by BuzzFeed: