Charlie Day Jokes About Playing Luigi in 'Top-Secret' Super Mario Bros. : 'This Is Serious Stuff!'

Morgan Lieberman/Getty Charlie Day

Charlie Day is under orders to remain tight-lipped about his upcoming Super Mario Bros. movie.

On Wednesday, the actor appeared on Jimmy Kimmel Live! where he touched on playing Luigi alongside Chris Pratt as Mario in the forthcoming animated film.

"I'm playing Luigi. In fact, I was just recording that this morning and I'd love to tell you all about it but they're top secret about this stuff," Day, 45, told host Jimmy Kimmel. "This is serious stuff! These are Nintendos people."

When Kimmel asked him if he had read the script for the film, Day said, "I know nothing, I show up and they say: 'You say this, and you say that,'" before adding that from what he could gather the movie was "very funny."

"Mario's probably in the know but they don't tell Luigi anything," he said, laughing.

RELATED: Chris Pratt, Anya Taylor-Joy, Jack Black and More Join Animated Super Mario Bros. Movie

And while Pratt might be playing his character's best friend in the film, Day revealed the two had not met while voice recording for the movie.

"We go in one at a time. Maybe they just don't trust me around Pratt," he added. "I don't even know if I'm really in the movie!"

In a September Instagram post, Pratt referenced the memorable "It's-a me, Mario" tagline and said of his voice for the project, "You'll have to wait to hear the voice, but we've been working hard at it." He also added that "dreams come true," while explaining his childhood connection to the games.

Never miss a story — sign up for PEOPLE's free daily newsletter to stay up-to-date on the best of what PEOPLE has to offer, from juicy celebrity news to compelling human interest stories.

The movie also stars Anya Taylor-Joy as Princess Peach, Jack Black as Bowser, Keegan-Michael Key as Toad and Seth Rogen as Donkey Kong.

Also a part of the cast are Fred Armisen as Cranky Kong, Kevin Michael Richardson as Kamek and Sebastian Maniscalco as Spike. The movie will also include a cameo from Charles Martinet, who voiced Mario and others in the video game series since the 1990s.

The Lego Movie 2: The Second Part screenwriter Matthew Fogel will pen the script.