The actor also opened up about his 'natural' chemistry with co-star Brad Pitt.
In Once Upon a Time in Hollywood, Leonardo DiCaprio plays a washed-up actor whose star is dimming as the tides of show business turn and he's unable to keep up.
Unlike his on-screen counterpart, DiCaprio himself has enjoyed unmitigated success throughout his career, earning piles of accolades and wild popularity -- and the 44-year-old actor acknowledges how fortunate he's been.
"This is a rare sort of occurrence. Hollywood's changing in a lot of ways. This is an art film that's a throwback to different type of filmmaking. And to sit back and look at [my past self] and be able to say that I'm able to still do this and be a part of a film like this, it's pretty humbling," DiCaprio told ET's Keltie Knight at the star-studded Los Angeles premiere of Once Upon a Time in Hollywood on Monday, after taking a look at his first interview with ET back in 1990.
"I feel lucky, is what I feel," he added with a smile. "I feel lucky to be an actor who's been able to work this long."
In the new Quentin Tarantino period drama -- set in Hollywood in 1969, amid changing times in show business and the specter of political and social unrest -- DiCaprio stars as Rick Dalton, while Brad Pitt plays his best friend and stunt double, Cliff Booth.
While the pair are best friends of many, many years in the film, DiCaprio said the chemistry between himself and Pitt "really came naturally."
"We both live in Los Angeles and this is about the changing of the culture in the late '60s, and we understand these dynamics of these professional relationships that also turn into families," DiCaprio explained.
The star said that he and Pitt were able to immediately embody their characters "as soon as we stepped into these shoes."
"Quentin gave us this amazing backstory of our characters and what we've been through and it was one of the more easy, sort of natural fits that I've ever experienced," he reflected. "Because we kind of knew who these guys were."
Once Upon a Time In Hollywood -- which also stars a massive ensemble cast including Margot Robbie, Al Pacino, Timothy Olyphant, Austin Butler, Dakota Fanning, Kurt Russell, the late Luke Perry and many others -- hits theaters July 26.
Brad Pitt and Leonardo DiCaprio Are Old Friends at 'Once Upon a Time in Hollywood' Photocall at Cannes