Ronan turned out to be a highly gifted prodigy, and started attending college when he was 11 years old.
"Mia drove him every day to Bard College, which is 90 minutes each way," Orth said. "She told me that she herself got a college education because he was so excited about going to school that he would tell her the whole -- everything that he had learned during the day on the way home."
He went on to graduate from Yale Law School at age 21 and won a prestigious Rhodes scholarship.
But 20 years after Farrow discovered Allen's relationship with Soon-Yi, Ronan remains estranged from Allen, who eventually married Ronan's adoptive sister.
Last year, Ronan tweeted "Happy father's day – or as they call it in my family, happy brother-in-law's day." His mother retweeted him, adding a simple word: "Boom."
Orth also interviewed another of Farrow and Allen's children, their adoptive daughter Dylan, for her Vanity Fair interview. Now 28, Dylan spoke publicly for the first time about an alleged incident that arose during a heated custody battle. There were allegations that Allen sexually abused Dylan in the attic of the family home when she was 7 years old, which Allen strongly denied.
"These totally false and outrageous allegations have sickened me so that I felt for the sake of all three children I must try to remove them from an atmosphere so unhealthy it can truly leave irreparable scars," Allen told reporters in 1992 when the allegations were first investigated.
"According to what Dylan told me, she truly is terrified of Woody Allen to this day," Orth told "Nightline." "She can't bear to even look at one of his pictures in a magazine.
When asked if Dylan explicitly told Orth that Allen molested her in the attic, Orth said, "She told me that she remembers very clearly what happened to her in the attic and what she was wearing when she got there and what wasn't on when she left. ... And so then she told me, 'my advice to the 7 year old Dylan today would be "be brave, testify."'"
When asked again to clarify whether Dylan told Orth if she had been molested and not just that she was made to feel uncomfortable, Orth said, "She told me that she was made to feel very uncomfortable."
Woody Allen's representatives told "Nightline" that Allen continues to categorically deny those charges. They pointed out that at the time, doctors at the Child Sexual Abuse Clinic at Yale New Haven Hospital conducted an investigation, interviewing Dylan, her parents and their nannies, and that they concluded that, in their opinion, Dylan had not been sexually abused.
"There are only two people who know what happened in that attic, Woody Allen and Dylan," Orth said. "They are the only two people."
Criminal charges were never filed against Allen, though in the early '90s, Frank Maco, the Litchfield County (Connecticut) state's attorney at the time, issued a statement saying he did not want to risk exposing Dylan, whom he called the "child victim," to the criminal process. But Allen did lose his custody battle and was only allowed supervised visits with his children.
"Woody went through four different legal proceedings to try to get visitation rights and more visitation rights with both Ronan and Dylan, and Ronan did not want to have anything to do with it," Orth said.
We may never know what happened between Allen and his kids, but what is known is that they are seemingly devoted to their mother.
Ronan and his mother are extremely close and travel the globe to crusade for humanitarian causes together.
"Mia did a very unusual thing. She took in four biological children and 10 adopted children, some with very severe physical and emotional difficulties, and she was able to meld them into a whole family," Orth said. "Of the eight that I talked to, they all said that they were very proud to be part of that family that they consider themselves to be cool and unique."
As to the identity of Ronan's father, Ronan responded to the Vanity article Tuesday with a wink, tweeting, "Listen, we're all 'possibly' Frank Sinatra's son."