The next generation royals were at the premiere after they filmed secret cameos last year. William told the crew that he was a "total Star Wars geek," The Daily Mail reported.
The "Today" show reported that one of the film's stars, John Boyega, confirmed the brothers filmed secret cameos. They play Stormtroopers in the eighth installment of the "Star Wars" franchise.
They were presented their own Stormtrooper helmets before the film rolled.
The Stormtrooper costume also reportedly hides the identity of other cameos. Tom Hardy and Gary Barlow are also among the identical helmets, The Telegraph reported.
They apparently filmed a scene with Daisy Ridley and Boyega, The Daily Mail reported.
This won't be the first time a famous face was featured in an unassuming role. Fans already know Daniel Craig appeared in "Star Wars: The Force Awakens," CNN reported.
“Star Wars: The Last Jedi” officially hits theaters on Friday, but some cities will have screenings as early as Thursday.