Green Book also gave Mahershala Ali his second best supporting Oscar win besides its win in the Best Original Screenplay category.
In a surprise win, Peter Farrelly's biographical comedy-drama "Green Book", received the Best Picture honour at the 91st Academy Awards upstaging award season favourite "Roma".
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The film, featuring Viggo Mortensen and Mahershala Ali, was based on the real-life story of Dr Don Shirley, an African-American jazz pianist and composer, who embarks on a cross-country tour that necessitates hiring a white driver Tony Vallelonga (Mortensen) to assist him as a bodyguard while he travels through America's racially-divided Southern states.
"Green Book" stopped "Roma", Mexican filmmaker Alfonso Cuaron's black-and-white love letter to his childhood, from making a clean sweep at the Oscars where it had already won Best Cinematography, Best Director and Best Foreign Language Film trophies.
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Other films nominated in the category were "Black Panther", "Vice", "BlacKkKlansman", "Bohemian Rhapsody", "The Favourite" and "A Star Is Born".
Hollywood star Julia Roberts presented the top honour of the ceremony to the cast and crew of the film including director Farrelly, actors Mortensen, Ali and Linda Cardillini.
"The whole story is about love. This is about loving each other despite our differences and finding out about the truth of who we are, we are the same people," Farrelly said while accepting the award.
He gave a shout out to Mortensen, saying, "We have no movie (without you). All these awards are because of Viggo and Mahershala and Linda but it all started with Viggo. I give you this my friend."
The director also thanked veteran filmmaker Steven Spielberg who had helped the film's producers in getting a distributor.
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Producer Jim Burke said the team put their heart and soul in the film.
"We made this film with love and we made it with tenderness. We made it with respect. It was all under the direction of Pete Farrelly," he said.
Apart from the biggest award of the night, "Green Book" also gave Ali his second best supporting Oscar win besides its win in the Best Original Screenplay category.
"Green Book", one of the most critically-acclaimed projects of the year, had a rough Oscar campaign, courtesy controversies involving Mortensen, Farrelly and the film's writer Nick Vallelonga, son of real-life Tony Vallelonga.
Mortensen, 60, had come under fire on social media for using the N-word during a panel discussion after the screening of the film, while Farrelly found himself embroiled in a controversy after an old report resurfaced where he admitted to flashing his privates as a joke.
Following the revelation, the director had issued an apology.
Even Vallelonga faced backlash when his old tweets resurfaced in which he claimed to have witnessed thousands of Muslims in New Jersey celebrate the September 11 attacks on the World Trade Center, which turned out to be a fake news.