Soon-Yi Previn has broken her silence for the first time in decades to launch a no-holds-barred attack on her estranged adoptive mother, Mia Farrow.

The 47-year-old Previn — who infamously married her mum’s former lover, 82-year-old director Woody Allen — blasted the Rosemary’s Baby actress as an abusive tyrant who beat her with hairbrushes, called her “moronic” and would hold her upside down “because she thought . . . that blood going to my head would make me smarter or something.”

“I was never interested in writing a ‘Mommie Dearest,’ getting even with Mia — none of that,” Previn told New York magazine in an explosive interview.

But she said she couldn’t sit by and let Farrow, 73, manipulate the #MeToo movement to exact her twisted payback against Allen.

“What’s happened to Woody is so upsetting, so unjust,” Previn said, referring to renewed press about sexual-abuse allegations leveled against him by his and Farrow’s daughter, Dylan Farrow.

Previn said her fraught relationship with her adoptive mother sprung from something close to hatred at first sight, from the moment Farrow, with camera in hand, picked up the 6-year-old at a Korean orphanage in May 1977.

“I remember the second I laid eyes on her,” Previn recounted to the magazine. “She came to me, and she threw her arms around me to give me a big hug. I’m standing there rigidly, thinking, ‘Who is this woman, and can she get her hands off of me?’

“She didn’t ring true or sincere.”

Previn, a runaway at age 5, was free from the hardscrabble streets of Seoul — where she described eating a bar of soap out of desperation and hunger — and the nun-operated orphanage, but her troubles at the hands of Farrow began before they even left Korea, she claims.

“I’d never taken a bath by myself, because in the orphanage it was a big tub, and we all got in it,” she said.

But on her first night with Farrow in their hotel room, “Instead of doing what you do with an infant — you know, maybe get into the water, put some toys in, put your arm in to show that you’re fine, it’s not dangerous — she kind of just threw me in,” Previn said.

“Mia wasn’t maternal to me from the get-go.”

Previn went to live with Farrow and her then-husband, the composer André Previn, and their blended brood in England. There were six siblings in all, including the couple’s biological children — Matthew, Sascha and Fletcher.

“There was a hierarchy — [Farrow] didn’t try to hide it, and Fletcher was the star, the golden child,” Soon-Yi Previn recalled. “Mia always valued intelligence and also looks, blond hair and blue eyes.”

Meanwhile, she and her adopted siblings were treated like “domestics,” Previn said.

Then the spasms of abuse, both physical and verbal, started, Previn claimed.

“She tried to teach me the alphabet with those wooden blocks,” she said. “If I didn’t get them right, sometimes she’d throw them at me or down on the floor.”

Farrow slapped her adopted daughter across the face and spanked her with a hairbrush, often while calling her “stupid” or “moronic,” Previn claimed.

She also recalled an incident in which Farrow hurled a porcelain rabbit at her.

“I could see from the expression on her face that she felt she had gone too far,” Previn said. “Because it could have really hurt me.”

When Farrow and André Previn divorced in 1979, Farrow uprooted most of the family, including Soon-Yi, to New York, where a new man soon entered both of their lives: Allen.

The 10-year-old Previn’s initial appraisal of the renowned director was not unlike the one she had of her mom.

“I hated him because he was with my mother, and I didn’t understand why anyone could be with such a nasty, mean person,” Previn said.

Allen hardly endeared himself to Previn when she overheard him telling Farrow that the pre-teen “should see a shrink.”

“And I’m thinking the most famous neurotic is saying this — and this is how he makes his living, being shy!” she told New York. “I hated him before, but I hated him double for saying this.”

Their frosty relationship began to thaw when Previn broke her ankle in the 11th grade, and Allen offered her a kindness she wasn’t accustomed to receiving from Farrow, urging her to go the doctor and driving the hobbled teen to school, she said.

The unlikely pair began to spend more time together — ironically at Farrow’s suggestion, Previn said.

They became regulars at Knicks games, and one night in the autumn of 1991, found themselves huddled watching an Ingmar Bergman film together.

“We chatted about it, and I must have been impressive because he kissed me, and I think that started it,” Previn said. “We were like two magnets, very attracted to each other.”

Previn and Allen talked early on in their relationship about what might happen if Farrow ever found out about their romance, but they decided it was nothing to worry about because it was a “fling” she would grow out of.

Their hand was forced in January 1992, when Farrow found nude photos of her adoptive daughter, left by an absent-minded Allen in plain view on a mantel.

The discovery sent Farrow into a tailspin, with her throwing the daughter out of their home, cutting her off from her college fund and falsely claiming to Allen that Previn was suicidal, according to Previn said.

That summer, Farrow alleged that Allen had sexually abused their young adopted daughter, Dylan.

The bombshell claim has been consistently denied by Allen — and deemed invalid by a team of child-abuse experts at Yale-New Haven Hospital — but it was enough to convince a judge to grant custody of the couple’s children to Farrow and saddle Allen with salacious allegations that plague him to this day.

Farrow “has taken advantage of the #MeToo movement and paraded Dylan as a victim. And a whole new generation is hearing about it when they shouldn’t,” Previn said.

Journalist Ronan Farrow — son of Mia Farrow and Allen — has been a leading voice in the tidal-wave movement.

But Allen and Previn, who wed in 1997, are still going strong and maintain that their love is the real deal.

Their relationship was a “huge betrayal [of Farrow] on both our parts, a terrible thing to do, a terrible shock on her,” Previn said.

“That’s what Mia must be most shocked about,” she said of the fact that she and Allen are still together. “This is so foreign to her.”

Farrow did not comment to New York magazine for the story.

Dylan Farrow, responding in a statement, called Previn’s assertion that she was pushed by her mother to speak out “offensive.”

“This only serves to revictimize me,” she said. “Thanks to my mother, I grew up in a wonderful home.”