Vallelonga released a statement to ET on Thursday apologizing for the offensive tweet and promising to "do better in the future."
"I want to apologize. I spent my life trying to bring this story of overcoming differences and finding common ground to the screen, and I am incredibly sorry to everyone associated with Green Book," said Vallelonga. "I especially deeply apologize to the brilliant and kind Mahershala Ali, and all members of the Muslim faith, for the hurt I have caused."
Vallelonga based the screenplay on the true story of the relationship between his father, Frank "Tony Lip" Vallelonga (played by Viggo Mortensen), and jazz pianist Dr. Don Shirley (played by Ali).
"I am also sorry to my late father who changed so much from Dr. Shirley’s friendship and I promise this lesson is not lost on me," Vallelonga continued. "Green Book is a story about love, acceptance and overcoming barriers, and I will do better."
In the offending tweet, posted to the writer's since-deleted account, Vallelonga agreed with an entirely false statement, made by then-Presidential candidate Donald Trump, who claimed to have seen people, who he implied were Muslim, cheering when the World Trade Center towers collapsed during the 9/11 terror attack.
"100% correct," Vallelonga reportedly replied to Trump. "Muslims in Jersey City cheering when towers went down. I saw it, as you did, possibly on local CBS news."
This claim has since been debunked and no factual evidence exists to support it, nor was any such mass cheering ever recorded or aired by any news stations at the time.
The controversy surrounding the Green Book writer comes amid backlash against the film's director, Peter Farrelly, over a resurfaced article from 1998 recounting stories of how the filmmaker used to flash his genitals at cast and crew members in the guise of a "prank."
"True. I was an idiot. I did this decades ago and I thought I was being funny and the truth is I’m embarrassed and it makes me cringe now," the director said in his statement to ET on Wednesday. "I’m deeply sorry."