Diego Luna on Filming 'Rogue One' in Secret Over 'Two Years'

PHOTO: A Star Wars Story: Jyn Erso (Felicity Jones) and Cassian Andor (Diego Luna).PlayJonathan Olley
WATCH Diego Luna Talks New 'Star Wars' Movie on 'GMA'

When Diego Luna was 6 years old, he watched the very first "Star Wars" movie, "A New Hope."

Interested in Star Wars?

Add Star Wars as an interest to stay up to date on the latest Star Wars news, video, and analysis from ABC News.
Add Interest

The Mexican-born actor was instantly hooked.

"Since then, it's been part of my dreams ... I've been dreaming to be part of this world all my life," he told ABC News.

But "Rogue One" is not your normal "Star Wars" movie. The standalone film does not require a deep understanding of the previous films.

"This film happens right before the very first film that was shot in 1977," he said. "You don't need to see the other ones to understand this one, which is good. It's the most modern 'Star Wars' film, obviously because it was made this year, but not just because of that. Because this is the only film of 'Star Wars' that can actually be different. That is the idea, in fact, it has to be different to all of the others. It's quite a unique stand, this one."

Luna had to be sequestered for periods of time and was forbidden from sharing details of the plot.

The movie, which arrives in theaters on Dec. 16, focuses on how the Rebels steal the Death Star plans -- a weapon of the Empire's that Luke Skywalker ultimately destroys in 1977's "A New Hope."

And yes, Darth Vader is back.

"You basically have to stop your life for two years, just get immersed into this world. You cannot tell anyone where you are living, so it's kind of easy to go crazy. The secrecy around this project is insane," he said.

But it's also "very special," he added. "Just being able to be part of a film that matters to me as a fan, you don't get that very often."

He also dished on some secrets about his character.

"He's an agent, an intelligence agent, he's a captain for the rebellion," he said. "He's in charge of the mission and this is the most dangerous, the craziest mission ever for the rebels, he has to put together this team ... he has to make sure they stay together."

The best part of his arsenal, Luna said, is the "three-piece rifle" he carries.

"It goes from a pistol, very cowboy looking, then it has three other pieces and become a precision rifle," he said. "[When filming] it took me a bit to find the way to do it fast and look like I knew what I was doing."