Brad Pitt and Leonardo DiCaprio star in Quentin Tarantino's new film

Director Quentin Tarantino. Photo / AP

Sony Pictures has confirmed that Quentin Tarantino's ninth film, about the Charles Manson cult murders, has finally found its A-list leads: Brad Pitt and Leonardo DiCaprio.

Once Upon a Time in Hollywood, set to hit theatres in August 2019, will follow former Western star Rick Dalton (DiCaprio) and his stunt double Cliff Booth (Pitt). The washed-up duo struggle to find work in 1969's free-spirited Hollywood, an environment in which Rick's neighbour, actress Sharon Tate, thrives. Given the year, we can guess what happens next.

The title appears to pay homage to Sergio Leone, the Italian director of Once Upon a Time in America and Once Upon a Time in the West, who is often credited with creating the spaghetti Western genre.

"I've been working on this script for five years, as well as living in Los Angeles County most of my life, including in 1969, when I was 7 years old," Tarantino said. "I'm very excited to tell this story of an LA and a Hollywood that don't exist any more."

It will be DiCaprio's second outing with Tarantino after playing slave-owner Calvin Candie in 2012's Django Unchained. Pitt worked with the director on Inglourious Basterds in 2009, when he played a Nazi hunter.

Though the role has not officially been cast yet, it is rumoured that Margot Robbie has been asked to play Tate.

Members of Manson's cult brutally murdered the actress on August 9, 1969, exactly 50 years before the scheduled release of Tarantino's film.

Tate was weeks away from giving birth to a child with husband Roman Polanski, who was charged eight years later with drugging and raping a 13-year-old girl. Controversially, Polanski is likely be a character in the movie.