For the last ten years, whenever anyone asked Katharina Kubrick— stepdaughter of the late, legendary filmmaker, Stanley Kubrick—about her youngest step-sister Vivian, her response was, “Oh, she’s living in L.A., doing something.” Their mother, Christiane Kubrick, would say the same thing.

“We weren’t lying, we were just being economical with the truth,” Katharina says over the telephone from the Kubrick’s Hertfordshire manor house, Childwickbury, where she and her mother teach art. “Because if you say, ‘My sister has become a Scientologist,’ where do you go from that?”

“We weren’t lying, we were just being economical with the truth,” says Katharina Kubrick. “Because if you say, ‘My sister has become a Scientologist,’ where do you go from that?”

But now, the Kubricks, a famously private family, are ready to break their silence about Vivian, who is now 50, and who stopped communicating with her family after joining the Church a decade ago. The silence is presumably part of a Scientology policy known as “disconnection,” ex-Scientologist Amy Scobee told The Daily Beast, which calls for members to cut ties with people close to them who are seen as antagonistic toward the Church. (A person close to the Church, who did not wish to give their name, said that disconnection was advised only when individuals were “attacking” the Church, and denied that the Church encouraged severing ties with family members.) But Christiane recently told the Guardian, “I’ve lost her. You know that? I used to keep all this a secret, as I was hoping it would go away. But now I’ve lost hope. She’s gone.”

Of the three Kubrick children—Vivian and Anya, who died last year, are Stanley Kubrick’s blood daughters; Katharina is from Christiane’s previous marriage—Vivian looked poised to be a protégé. At 17, she made a documentary about the making of the Jack Nicholson thriller The Shining; at 24, she composed the score for Kubrick’s Vietnam homage, Full Metal Jacket. But she cut ties with her dad just before he died, while he was editing the Tom Cruise-Nicole Kidman erotic epic Eyes Wide Shut. “Stanley asked Vivian to compose the score, but at the last moment she said she wouldn’t,” Christiane told the Guardian. “They had a huge fight. He was very unhappy. He wrote her a 40-page letter trying to win her back. He begged her endlessly to come home from California. I’m glad he didn’t live to see what happened.”

Kubrick died the same year that film was released, in 1999. When his funeral was held in England, Katharina says that Vivian showed up with a Scientology member—presumably a “handler,” according to Scobee. The person sat on a bed, saying nothing, while Vivian complained of back pain that she said had been caused 10,000 years ago.

“The whole situation was so impossibly weird,” Katharina recalls of the last time she saw her sister. “We didn’t know, at first, anything about it really, so we were like, ‘Who is this person? Why won’t they talk to us?’

Last year, Katharina and her mother were hoping to reconcile (or at least reconnect) with Vivian, when Anya passed away from cancer. Vivian did not come to England for the funeral, despite the fact that growing up, she and Anya had been “inseparable,” according to Katharina. Nor would she meet with her mother and Anya when, earlier, they came to California seeking treatment for Anya. “She was very reluctant,” says Katharina. “She has completely changed as a person. And it’s just very sad. We’re not allowed to contact her… Something happened to her. She has been changed forever.” She pauses. “I hope not forever.”

Attempts to contact Vivian through the Church of Scientology—which had no official comment for this story—were not successful. But Stephanie Bennett, a professional dog trainer, got to know Vivian when she helped her tame a stray German Shepherd a few years ago. (Vivian is an animal lover who, as a child, reprimanded Steven Spielberg for not treating snakes well on the set of Raiders of the Lost Ark.) When Bennett knew Vivian, she was living a quiet life in Hollywood.

“She seemed to be very private. She would talk on the phone to friends, but didn’t go out a lot except for the church,” Bennett said of the time she spent with Vivian. “I know she was very wary of lots of things in the world. Where her money was going, who was involved—all that stuff was just very private.”

She said that Vivian did not talk about Scientology, but that there was literature around Vivian’s house, which had a music studio set up in it, and which was located in close proximity to the Celebrity Centre on Franklin Avenue. She also did not talk about her family, with the exception of her late father.

“It seemed that she really missed him. That his death was hard for her.”

Bennett said she would send an email to Vivian to see if she would talk to The Daily Beast, but never got back to me.

According to Katharina, who is six years older than Vivian, her sister was “the cute, funny, and talented baby of the family.”

She was also the daughter that seemed most likely to follow in her father’s footsteps. Born as he was finishing up Spartacus, at six she starred in 2001: A Space Odyssey, as Dr. Floyd’s daughter, Squirt. While he was editing the film in the basement of the MGM building in New York, Vivian was scuttling around the cutting room floor, demanding chocolate doughnuts from the Sixth Avenue Deli. And in what Stanley Kubrick biographer Vincent Lobrutto describes as a “rare breach of intense security,” father allowed daughter to document him making The Shining. She was rumored to have plans to make a similar documentary about Full Metal Jacket, but that never came to pass.

Stanley Kubrick “wanted her to get serious” about filmmaking, says Katharina. “He was only too thrilled when she was busy and being creative, and not sitting on her ass. We are a family of do-ers and makers and getting on with things.

“Viviane is immensely talented and she could have more or less done whatever she wanted,” Katharina continues. “But I guess, like a lot of people, she was looking for something. Obviously, she thinks she’s found it.”

She describes her sister as a rebellious spirit who “did a lot of alternative stuff” like Tarot cards, crystal healing, and homeopathy, and said she thinks she was first introduced to Scientology while working on the score for the 1999 film The Mao Game, starring Kirstie Alley, a Scientology member. (The Scientology anonymous source said that Vivian got involved in the Church in 1995, but not through Alley.) Both Katharina and her mother deny that Tom Cruise, another celebrity Scientologist, had anything to do with Vivian joining the church, despite the Eyes Wide Shut connection.

Alley’s manager did not respond to an email seeking comment from Alley.

Paul Joyce, a filmmaker who’s made four documentaries about Kubrick, says he last saw Vivian at a dinner in Los Angeles in the mid-1990’s.

“The impression I got was that she and Stanley had been extremely close, but that they were then not in contact that much,” he says in a telephone interview. “I got the very strong feeling that the severing of her relationship with her father and family had come as a result of her decision to move to L.A.”

“It doesn’t surprise me that she turned to Scientology,” Joyce continues. “It seemed to me like she was in need of some kind of assistance. Stanley was a very strong father. I don’t mean in terms of directing her every move, but as a presence. And to go away from that, something pretty powerful has to fill that void. So my feeling would be that Scientology equals Stanley.”

Plus: Check out more of the latest entertainment, fashion, and culture coverage on Sexy Beast—photos, videos, features, and Tweets.

Nicole LaPorte is the senior West Coast reporter for The Daily Beast and the author of The Men Who Would Be King: An Almost Epic Tale of Moguls, Movies, and a Company Called DreamWorks.