The film - Tarantino's ninth - has been years in the making and stars Tinseltown A-listers Leonardo DiCaprio, Brad Pitt and Margot Robbie, alongside the likes of Al Pacino, Kurt Russell and Dakota Fanning.
It tells the tale of former TV actor Rick Dalton (DiCaprio) and his stunt double Cliff Booth (Pitt), following their attempts to break into the film industry during 1969 in LA - right at the time of the famous Manson Family murders.
In the new, full-length trailer we see our first proper glimpse of Damon Herriman as the infamous Charles Manson - the blink-and-you-miss-it appearance he made in the teaser trailer.
Turning towards the camera with a VERY creepy smile, it already looks like he's nailed the role.
We also see more of Margot Robbie as Sharon Tate, the wife of director Roman Polanski - who's proudly telling someone about her role in a movie.
"I'm Sharon Tate," Robbie says excitedly.
"I'm in the movie! I play Miss Carlson, the klutz."
Then there's Hollywood veteran Pacino, who's clearly still got it.
Looks like we're also about to witness one of cinema's greatest bromances unfold, with the bond between Rick and his stuntman Cliff already evident from short clips of their friendship we see in the trailer.
In a press release issued last year, Tarantino explained that the story takes place 'at the height of hippy Hollywood'.
"The two lead characters are Rick Dalton (DiCaprio), former star of a western TV series, and his longtime stunt double Cliff Booth (Pitt)," he said.
"Both are struggling to make it in a Hollywood they don't recognise anymore. But Rick has a very famous next-door neighbour... Sharon Tate."
He continued: "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 seven years old.
"I'm very excited to tell this story of an LA and a Hollywood that don't exist anymore. And I couldn't be happier about the dynamic teaming of DiCaprio and Pitt as Rick and Cliff."
Yesterday Tarantino issued an open letter to all those who'd be catching the premiere of the film at Cannes this week, urging them not to spoil it for others yet to watch it.
Captioning the message #NoSpoilersInHollywood, he wrote: "I love cinema. You love cinema. It's the journey of discovering a story for the first time.
- Once Upon a Time in Hollywood (@OnceInHollywood) May 20, 2019
"I'm thrilled to be here in Cannes to share Once Upon A Time In Hollywood with the festival audience.
"The cast and crew have worked so hard to create something original, and I only ask that everyone avoids revealing anything that would prevent later audiences from experiencing the film in the same way."
After premiering at Cannes Film Festival this week, Once Upon A Time In Hollywood will be released on 26 July in the US and on 15 August in the UK.