We’ve seen Will Smith face off against everything from aliens to evil elves throughout his blockbuster film career, but his latest action flick has him up against his most formidable enemy yet: his younger self.

Set for release Oct. 11, Gemini Man puts Smith in the role of Henry, an elite, aging assassin who is hunted down by Junior, his clone who happens to be a few decades younger. Smith plays both characters, who are 50 and 23 years old, respectively, via a new CGI process that the filmmakers are touting as revolutionary.

“The level of work is so spectacular it’s hard to get people to understand,” Smith said this week at a press preview of the film. “The special effects people at [special effects studio Weta Digital] have done something that has really never been done before.”

As director Ang Lee explained at a press preview of the film this week, the idea for Gemini Man has been around for more than two decades. However, executing the idea was limited by technology until recently, when filmmakers developed a motion capture process that helped them create a younger, digital version of Smith using a motion capture process, as VFX supervisor Bill Westenhofer explained in a newly released featurette.

“This is not de-aging. This is not face-replacement,” Westenhofer said. “What you see for Junior is a completely digital creation 100% driven by Will Smith’s performance.”

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Smith even appeared as his younger self in a promo for the film posted to his popular YouTube account in which he tells himself to “come back to Philly a lot” before debuting a new trailer for Gemini Man.

However, despite the technological challenges, one of the film’s biggest hurdles was the human element. Specifically, as Lee said this week, Smith is “a much better actor today than 30 years ago,” and as a result, the director needed the Philly native to subdue his acting chops when playing his younger self.

“Ang would show me some of my old performances and he’d say, ‘Look at this. That’s not good, I need you to do that,’” Smith said. “So I got to see all of the tragedies that I committed in entertainment.”

According to producer Jerry Bruckheimer, the process led to Smith delivering an “Academy Award-winning performance” in the film. If Bruckheimer is right, Smith could receive his first the first Oscar of his career.