Authenticity is the heart and soul of the new biopic "Bruce Lee, My Brother," the early life story of the man who put Hong Kong action films on the map, its director told The Hollywood Reporter.

As its title declares, the film pieces together the superstar's childhood -- Lee would have turned 70 on Sunday -- and young adulthood from the memories of his four surviving siblings, Phoebe, Agnes, Peter (who died in 2008) and Robert.

"The Lee family supplied us with all the details and the tidbits of their family life," director Raymond Yip said. "So we took great care to be loyal to the truth and avoid anything that felt fake, which made it rather difficult for us in terms of creating the structure of the script. But the Lee family was very pleased with the result, especially with how close it was to what actually happened."

The biopic took years to put on the screen, not least because of the difficult task of finding a young actor to play the role of the iconic megastar. "We've been on the lookout for a possible candidate all over China since 2008, but no one could capture the Hong Kong spirit of the young Bruce Lee," Yip explained.

But when writer-director team of Alex Law and Mabel Cheung, invited the film's producer, Manfred Wong, to a screening of their opus "Echoes of the Rainbow," the search was over. Aarif Rahman, a 23-year-old singer-songwriter who made his acting debut (and stole the show) in "Echoes," was locked in as the young Bruce Lee.

"Including Lee's brother Robert, we were quite amazed by how much Aarif resembles Bruce. No one can say for sure whether an actor really embodies Bruce's spirit except for his family. So it was a go from then on," Yip recalled.

The film began pre-production in March to push for a November 25 release in Hong Kong. The HK$36 million ($4.6 million) project has been snapped up by distributors in over 10 territories.

The Hong Kong-born Rahman, of Malay-Arab-Chinese ancestry, will have to shoulder any potential sequels for the Bruce Lee life story, said Yip.

"We certainly hope to continue telling Bruce Lee's story, but it depends on how this one is received, especially on the public reception of Aarif as Bruce Lee. Lee was a legendary figure. Who plays him in the film is the biggest issue for us as filmmakers. But I have faith in Aarif," Yip said.

Although the biopic tracks the early life of the kungfu master from his birth in San Francisco, old Hong Kong plays a key role. The film shows Lee and his friends as fixtures in the mid-century Hong Kong film industry, allowing the filmmakers to reenact scenes from famous movies of the age.

"Bruce Lee grew up on soundstages. But the films-within-a-film were also a way for us to recapture the collective memories of the Hong Kong people," Yip said.