Woody Allen's son Moses has disputed allegations that his father molested his sister Dylan in 1992, claiming she was coached by their mother Mia Farrow.
"I can no longer stay silent as [Allen] continues to be condemned for a crime he did not commit," Moses Farrow wrote in a lengthy personal essay.
Farrow accused stars who have distanced themselves from his father of "rushing to join the chorus of condemnation".
In response, Dylan Farrow said the post was "beyond hurtful".
"This is an attempt to deflect from a credible allegation made by an adult woman," she wrote on Twitter.
"It's easily disproven, contradicts years of his own statements... and is part of a larger effort to discredit and distract from my assault."
Moses Farrow previously came to his father's defence in 2014, telling People magazine that Mia Farrow had created an "atmosphere of fear and hate towards him".
Farrow goes on to dispute his sister's claim that Allen sexually abused her when she was aged seven, during a visit to Mia Farrow's home in Connecticut.
He states that there were five children and three adults in the house at the time, insisting that "none of us would have allowed Dylan to step away with Woody".
Farrow claims his mother coached Dylan to make her allegation because she was "furious" about Allen having a sexual relationship with Soon-Yi Previn, her adopted daughter.
He goes on to call an occasion when he wrote and read out a letter condemning his father "the biggest regret of [his] life".
Colin Firth, Greta Gerwig and Rebecca Hall are among a number of stars who have expressed regret at working with the Oscar-winning film-maker.
Moses Farrow said their "fear of not being on the 'right' side of a major social movement" had led them to turn against him.
Prosecutors investigated Allen over the alleged 1992 incident and decided not to bring charges against him.
The 82-year-old has always denied the claims and accused the Farrows in January of "cynically using the opportunity afforded by the Time's Up movement to repeat this discredited allegation."
Moses Farrow, who was born in South Korea and adopted by Mia Farrow in 1980, is now a marriage and family therapist.
The BBC has asked Mia Farrow's representatives for comment.