Zac Efron gives Ellen DeGeneres a sexy lap dance

It's good to know Zac Efron gets starstruck too!

The Dirty Grandpa star is a guest on Wednesday's Ellen DeGeneres Show, where the 28-year-old admits working with a "legend" like Robert De Niro can be kind of intimidating.

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"Working with De Niro was really fantastic because I got to get to know the legend, but it was also really awkward at moments 'cause I've seen virtually everything this guy's done," he says. "I mean, I've seen every film, I can quote him verbatim in half of his movies, if I can even reach half. He's never seen a single thing that I've done, like at all."

See photos of Efron through the years:

When Ellen protests the notion, Zac counters, "What could [he] have possibly even seen that I would have been a part of? High School Musical?"

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OK, fair point. While HSM is a CLASSIC in its own right, it is hard to picture the two-time Oscar winner kicking back to watch it. Still, Ellen suggests that he might have seen Paperboy, Zac's 2012 film with Nicole Kidman that landed the actress a Golden Globe nomination.

"I'll tell you what, he didn't tell me if he did," Zac jokes about whether his Dirty Grandpa co-star had seen the film. "But that would be a good one."

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While working with a great like De Niro humbled the actor, he was not too shy to give Ellen a lap dance while playing a round of her popular "Heads Up" app game.

Watch Zac's impressive moves in the video below!