Director Ang Lee has explained why he digitally created a younger version of Will Smith for his latest film.

In Gemini Man, the 51-year-old Smith plays a hitman who does battle with a cloned version of his younger self, who was created to be the perfect soldier.

The depiction of the younger character was entirely digitally rendered, with Smith adding his voice months later.

The film was shot at a much higher frame rate than usual (120 frames a second rather than the usual 24) frames a second, which makes the action sequences much more visceral.

Arriving at a fan event for the film in Budapest, Lee, who has won directing Oscars for Brokeback Mountain and Life Of Pi, told PA:  "With this media you just cast a different person as him, it wouldn't work.

"You put different hair and make-up and act differently, that wouldn't work.

"You cast his son to play him, that wouldn't work, so it has to upgrade to what this media requires.

"It all comes together to do something new, to tell the story we couldn't tell before."

Describing the images of a younger Smith that he chose to base the new digital character on, Lee said: "It's a combination of Bad Boys (from 1995), which was the first time we see him being the movie star that we know, not a TV star but a movie star, that carries big things... and Six Degrees Of Separation (from 1993) where he shows he's a really fine sensitive actor and his performance is genuine, so the two are really put together as a really good reference."

Reflecting on Smith's longevity and appeal as a movie star, Lee said: "He's a good actor. Not all movie stars are good actors, and not all actors are good movie stars, they wish.

"But he's got the both of them and he's proven through his career he can act many things and people follow it, some bigger than the other, but we follow his career.

"It's pretty incredible, we are lucky to have him, he's the guy to do it."

Gemini Man hits cinemas on October 11.