Paramount Pictures

Will Smith faces off with his younger self in "Gemini Man" — a feat only possible thanks to advanced CGI technology.

A behind-the-scenes featurette reveals more details about Ang Lee's sci-fi thriller and how Smith was able to play both dual roles: an aging assassin hunting down his younger clone.

"This technology is going to change how movies are made," Smith says in the video.

But this is not the technology used to make Samuel L. Jackson look younger in "Captain Marvel," VFX supervisor Bill Westenhofer says.

“This is not de-aging. This is not face-replacement," he explains. What you see for Junior is a completely digital creation, 100 percent driven by Will Smith’s performance capture."

It's definitely an intriguing use of CGI — as the video shows, Smith is acting in the scene, even though he's playing his younger character. Hopefully, more info about how this movie magic works will be made available later.

As Smith says, "I couldn't have played Junior at 23 years old, but now I'm able to understand and capture both characters because of the amount of experience I've had as an actor."

"Gemini Man" opens in theaters October 11.