After Green Book won the Oscar, its screenwriter, Nick Vallelonga, said he didn’t really realize his father’s friend Don Shirley had a family.

His tone-deaf remarks ensured that a potent well of irritation and anger over the award of the Best Picture to Green Book bubbled over on online forums and social media.

Vallelonga, who is the son of the white character portrayed in the film, said he didn’t get in touch with the black classical pianist’s family because he “didn’t even know they really existed until after we were making the film.”

The son of Tony “the Lip” Vallelonga, who drove the musician on a tour of the Jim Crow-era Deep South in the 1960s, also claimed backstage that Don Shirley had told him not to get in contact with his family before his death, saying: “The Don Shirley family thing falls on me, but Don Shirley himself told me not to speak to anyone. He told me the story that he wanted to tell, he protected his private life and all other things about him, miraculous things about him.”

Vallelonga said, “He told me, if you’re going to tell the story, tell it from your father, me, don’t speak to anyone else. That’s how you have to make it.”

Vallelonga concluded his remarks by saying, “I kept my word to that man, I wish I could reach out to Don Shirley’s family, I really didn’t know they existed until we finished the film.”

The remarks are likely to go down badly with Shirley’s nephew Edwin Shirley III, who claims his uncle rejected the idea of a movie about his tour.

“I remember very, very clearly, going back 30 years, my uncle had been approached by Nick Vallelonga, the son of Tony Vallelonga, about a movie on his life, and Uncle Donald told me about it,” Edwin told the Shadow and Act website in December. “He flatly refused.”

Mahershala Ali, who won the Oscar for Best Supporting Actor, has apologized for not contacting Shirley’s family. They say the movie exaggerates Shirley’s relationship with his driver.

Critics have also questioned sequences in which the Tony character introduces Don to the music of Little Richard, and encourages him to eat fried chicken.

Spike Lee rose from his seat and walked to the back of the theater as the movie was crowned Best Picture. During the film’s victory speech, Lee reportedly had his back turned to the stage.

The awards for Green Book have led to angry and sarcastic exchanges on Twitter and other social-media platforms.