'What we see in the film is their relationship as actors, as friends over the past 40, 45 years'
Director Martin Scorsese on Friday praised the "magical" relationship between Robert De Niro and Al Pacino in the trio's new gangster epic "The Irishman."
The legendary film-maker has made headlines over the past month with his trenchant criticism of modern-day Hollywood superhero movies as "not cinema."
But at an American Film Institute tribute event in Los Angeles, Scorsese preferred to discuss the long-standing collaborations of his own generation.
"What we see in the film is their relationship as actors, as friends over the past 40, 45 years," he said. "There's something magical that happens there."
The nostalgic mob movie, released on Netflix on November 27, sees a former mafia hitman (De Niro) reflect on his violent life, including his relationship with a disappeared union leader (Pacino).
De Niro and Pacino co-starred - separately - in "The Godfather: Part II" (1974), before memorably sharing the screen in 1995's neo-noir classic "Heat."
Scorsese said trust between film-makers was essential, before quipping that they also "have to have some talent."
"The Irishman" is Scorsese's ninth film as director with De Niro, whom he has known since they were both sixteen.
The director said he had been reluctant to join with De Niro on another gangster movie after hits such as "Goodfellas" and "Casino" unless they could "go deeper."
But they joined forces again after finding the missing ingredient.
"It turned out just to be - us. We're 75, 76 years old now. You look back and you think about the things you did in your life, or the things you wish you wouldn't have."
"It was about time, it was about us looking back on our whole lives in the 60s and the 70s, and Hollywood and in cinema. And so that issue of time stayed with us," he added.
The film, which runs to three-and-a-half hours and cost a reported $160 million to make, is currently on a limited theatrical run.
It has been a decade in the making, and is seen as a favorite in a rapidly looming Oscars race.
The movie uses a new technology to digitally "de-age" its stars on screen.
Oscar-winner Scorsese, 76, was honored at the American Film Institute's AFI Fest, which runs in Los Angeles until November 21.