Zac Efron Raves About Shirtless Robert De Niro on 'Dirty Grandpa' Poster!

Robert De Niro holds a shirtless Zac Efron on his back for this new Dirty Grandpa poster.

The hunky 28-year-old actor is raving over his 72-year-old co-star’s body!

“No joke Robert De Niro is low key as strong as The Rock. First time I saw him shirtless he did over 25 pull-ups in a row and I couldn’t help but be entranced by his rippling back muscles,” Zac wrote on Instagram. “This picture is real by the way. Like he actually did that. #DirtyGrandpa January 22!”

See more posters below and watch the new trailer.