It was AncestryDNA’s customer-service rep who had to break the news to Catherine St Clair.

For her part, St Clair thought she was inquiring about a technical glitch. Her brother—the brother who along with three other siblings had gifted her the DNA test for her birthday—wasn’t showing up right in her family tree. It was not a glitch, the woman on the line had to explain gently, if this news can ever land gently: The man St Clair thought of as her brother only shared enough DNA with her to be a half-sibling. In fact, she didn’t match any family members on her father’s side. Her biological father must be someone else.

“I looked into a mirror and started crying,” says St Clair, now 56. “I’ve taken for granted my whole life that what I was looking at in the mirror was part my mother and part my dad. And now that half of that person I was looking at in the mirror, I didn’t know who that was.”

St Clair thought she was alone with her loss, and what an odd sort of loss it was. She had grown up in a tight-knit, religious family in Arkansas, never suspecting a thing. Her four older siblings loved her no less as a half-sister. One brother didn’t think it was a big deal at all. “He says he wouldn’t have been this upset if it happened to him,” she told me. “I don’t discuss this topic with him much anymore.” St Clair eventually found her biological father by tracing other matches on Ancestry’s website. He was a stranger her mother knew more than half a century ago. The DNA test didn’t erase her happy childhood memories, but it recast her entire life up to now.

The first time St Clair met someone who understood this—in the same bone-deep way she did—was online. She saw that Delilah, the popular radio host, had asked on her Facebook page if anyone had learned anything interesting from DNA tests. Well, sure, St Clair thought. She replied that she had just found out her dad was not her biological father. An hour later, a woman who saw the comment messaged her saying, “Oh my god I thought I was the only one.” For the next three hours, they feverishly sent messages back and forth. They cried. They shared their fears and anxieties. They realized they weren’t crazy for feeling those fears and anxieties. “By the time we finished talking, we were both emotionally drained,” St Clair said. “Nothing’s really changed for either of us but we feel better just because we had somebody to talk to.”

St Clair went looking for more people to talk to. She looked for support groups. She found none. So, being the type to take things in her own hands, St Clair started a group on Facebook called DNA NPE Friends, where NPE refers to “not parent expected.” (NPE comes from the genetic genealogy term “nonpaternity event,” which St Clair and others have refashioned to include both parents; another increasingly common term is “misattributed parentage.”)

“Each person comes into our group thinking they are a freak,” says St Clair. And then they find each other. A year later, DNA NPE Friends—just one of several secret Facebook groups for misattributed parentage—has amassed more than 1,000 members.

These are boom times for consumer DNA tests. The number of people who have mailed in their saliva for genetic insights doubled during 2017, reaching a total of more than 12 million. Most people are curious where their ancestors came from. A few are interested in health. Some are adoptees or children conceived from sperm donation who are explicitly looking for their biological parents. DNA testing companies like 23andMe and AncestryDNA regularly tout happy reunions on their websites.

But not all biological parents want to be found. In conversations and correspondence with more than two dozen people for this story, I heard of DNA tests that unearthed affairs, secret pregnancies, quietly buried incidents of rape and incest, and fertility doctors using their own sperm to inseminate patients. These secrets otherwise would have—or even did—go the grave. “It’s getting harder and harder to keep secrets in our society,” says CeCe Moore, a prominent genetic genealogist who consults for the television show Finding Your Roots. “If people haven’t come to that realization, they probably should.”

St Clair told me she sees it as a generational shift. The generation whose 50-year-old secrets are now being unearthed could not have imagined a world of $99 mail-in DNA kits. But times are changing, and the culture with it. “This generation right now and maybe the next 15 years or so, there’s going to be a lot of shocking results coming out. I’d say in 20 years’ time it’s going to dissipate,” she predicted. By then, our expectations of privacy will have caught up with the new reality created by the rise of consumer DNA tests.

But until then, hundreds, maybe thousands, of people like St Clair are left to piece together their family histories, containing the fallout of a DNA test however they can. The best help, many have found, is each other.

“It was better than therapy,” Dawn, 54, says of joining the DNA NPE Friends group. “I tried therapy. It didn’t work.” (The Atlantic agreed to identify by first name only the people who have not revealed their misattributed parentage to friends and family.) Therapists, friends—they all had trouble understanding why the revelation mattered so much. When Dawn told her close friends that her biological father had Italian heritage, they joked about making cannoli. “They don’t understand the gravity,” she says. She herself didn’t quite understand until it happened to her either. Dawn had spent her whole life suspecting her father was not her biological father, yet the revelation still left her unmoored. “The very foundation of who I thought I was was ripped out from under me,” she says. “Until that moment, I had no idea how much stock I had put in my family to identify and to find who I was.”

In the Facebook group that St Clair now runs with several admins, she does stress that the group is not a substitute for therapy. She advocates getting professional help, even describing to me at length over the phone how to find employee assistance programs for free counseling. But as the group’s creator, she has become a de facto tribe-mother-counselor-guru. Members of the group would repeat her mantras (We’re not a dirty little secret) back to me. And they often started sentences with “Catherine says… ” before reciting some bit of her advice.

I asked St Clair if she had any professional training for this, and she laughed, saying no. But she grew up in a family that fostered a lot of kids, and taking care of an adopted younger sister with cerebral palsy has taught her to let go of anger. And she reinforces this in the Facebook group, quickly deleting unsupportive comments. “Anger only hurts you,” she says. “That’s why I push so hard with my group.”

Lisa, 44, admits she is still trying to let go of that anger. She had always felt out of place in her family. Her hair—which she always straightened—was naturally fine and curly, her skin dark. “People would think I’m Hispanic, and would speak Spanish to me on the street,” she says. So when a DNA test in 2015 revealed her biological father was likely African American, it clicked into place. But her mom denied it. “She wouldn’t answer me. She would change the subject,” Lisa recalls. When she kept pressing, her mother broke down, saying it would destroy the family and that her dad—the man she grew up with—would kill her. She refused to say anything else about Lisa’s biological father.

Lisa doesn’t want to strain her relationship with the father who raised her either. “I just could never break his heart,” she says, but her mother’s refusal to talk frustrates her. Reading the same stories from other people about confronting their parent, Lisa says, has made it easier to cope. She’d like to to host a meetup with members of the DNA NPE Friends group who live near her in Pennsylvania.

Lisa has also set out on her own to find her biological father. “I just want to know who he is,” she says of her father. “I just want to see a picture.” The DNA test matched her with a cousin in California on her father’s side. By constructing “mirror trees”—a technique genetic genealogists use to find common ancestors—she thinks she found one of her grandparents, but she has not yet been able to pinpoint one man as her father.

Kathy, 55, also told me about her yearning to know more about her biological father. By the time she found out about her misattributed paternity from a DNA test, he had already passed away. She found Newspapers.com clippings about his old band from the 1940s. She visited the town where he grew up not too far from her. And when she learned an actor played him in a 1990s movie, she watched it intently, studying the actor for clues to the real man. “It’s the closest thing I had,” she says.

The revelation has not been easy for her mother, who Kathy suspects had an affair with her biological father when she was a secretary at his firm. It also caused a rift with her sisters, who are close to her mother. “My sisters were freaking out. They didn’t want me to say anything,” Kathy says. “They said keep it a secret. Why do you need know? Why open the door? Why open the can of worms?”

St Clair has a mantra for these situations, too. “I’m sorry,” she says, “I’m not a cause of the problem. I’m the result of it.” Still, she is sympathetic to the upheaval these revelations can cause. “You have to try to put yourself in the shoes of this person who’s about to be blindsided. There’s an adult out there that is their child that they never knew about. Maybe they had an affair at the beginning of their marriage and they changed their ways … this is going to cause a major tear in their family. It could. We always try to prepare for the worst.”

That’s why the DNA NPE Friends group offers detailed advice on how to make first contact. The group suggests going with a letter that asks for family medical information and makes clear that the writer is not after money. And send photos, ideally three of them: the person as a toddler, as a teen, and as an adult with their own family if they have one. “It strokes the ego to be able to say … oh my gosh she’s got my nose and my eyes. So it tugs at his heartstrings,” says St Clair.

Of course, the attempts to reach out are sometimes met with anger or radio silence. After Todd, 53, took an AncestryDNA test, he found some new cousins that he messaged on Facebook. The cousins ended up blocking him. “They think I’m after something,” he says. It was the group that talked him down, advising him to give it time and write a letter. When he contacted a newfound aunt, he also posted the letter to the group for editing advice.

Todd’s discovery was actually not about his own father but his mother’s father, and he’s still torn about whether to tell his mother. He remembers the devastation when he first realized his mother’s sisters were not his full aunts. “The second I found out I’m ashamed to say it felt different. I didn’t feel as close to them,” says Todd. “It was tears every day for nine months.” He’s made some peace with it now, but he worries that his elderly mother would take it harder. Todd wishes that AncestryDNA had given more of a warning. “They have that commercial where the guy’s like, ‘Now I don’t wear lederhosen’ [after finding out his ancestors were Irish rather than German]. That was your surprise. Let me tell you my surprise,” says Todd. “You can find something you really don’t want to know. I think they should issue that warning.”

Both 23andMe and AncestryDNA have warnings about uncovering unanticipated information about family in their terms of service. They also allow users to opt in or out of finding genetic matches, and 23andMe has another warning in the opt-in screen.

Lynn, 55, of all people, understood that DNA tests can reveal family secrets. Her husband had been adopted, and Lynn set out to use her son’s AncestryDNA tests to find his paternal grandparents. In the process, she compared her son’s results to her brother’s and quickly realized something wrong. It didn’t look like a typical uncle-nephew relationship. The reason, Lynn eventually found out, was that her biological father was not the father she grew up with. “I just didn’t see it coming,” she says. “If you go looking into other people’s secrets, you just might find one of your own.” Her mother still refuses to reveal what happened.

An AncestryDNA spokesperson said in a statement, “Almost everyone who takes our AncestryDNA test finds something surprising, and for most customers it’s something exciting and enriching; but there are certainly cases where a discovery might be quite unexpected … We also have a small, dedicated group of representatives who are specially trained to speak to customers with more sensitive queries.”

A 23andMe spokesperson added, “We typically counsel customers that while we’re confident in our ability to predict close genetic relationships, we’re not a paternity test.”

To join DNA NPE Friends, you first have to apply through a closed but public “gateway” group on Facebook. It’s a jury-rigged system, designed to get around the fact the group needs to be findable enough to reach new members but also secret enough so as to not broadcast my father is not my biological father to one’s entire social network. St Clair and her admins also privately invite people who post about misattributed parentage in two popular public groups on Facebook called DNA Detectives and DD Social, both run by Moore, the genetic genealogist. Moore also runs secret splinter groups dedicated to various specific scenarios like unknown paternity and incest.

Like any rapidly growing group with 1,000-plus members, DNA NPE Friends has had some growing pains. One particular post kicked up a firestorm, according to St Clair, when some sperm donor-conceived members of the group took it to suggest anonymous sperm donors don’t want to know their biological children. Some threatened to leave. St Clair says donor-conceived people are absolutely welcome in the group, and her admins aggressively weed out negative comments.

Brianne Kirkpatrick, a genetic counselor, also runs a couple of Facebook groups for people dealing with DNA surprises, and she deliberately keeps them small. Kirkpatrick’s groups are less active day to day, but they are also less impersonal because of their size. (Lynn, the woman whose attempt to find her husband’s parents revealed her own misattributed paternity, is a member of one of these groups.) Kirkpatrick also wants to maintain the privacy and confidentiality she promised her members, the first of whom she met through her genetic-counseling practice a few years ago.

Having watched the stories in the group unfold, Kirkpatrick emphasizes they aren’t all negative experiences—even if they start that way. “How people react in the short term will not necessarily predict the long term,” she says. St Clair put it to me in even more vivid terms. She compared finding out about the existence of a secret child to finding out your teenage daughter is pregnant. “Everyone’s tearful, upset. Excuse my phrase, the shit just hit the fan,” she says. “But nine months later they’re standing at the hospital goo-gooing and celebrating and passing out cigars and balloons.” It takes time.

When St Clair took her AncestryDNA test, the parents who raised her and her biological father had all passed away. She didn’t have to—or perhaps never got to—confront them. But she did realize that one of her genetic matches on AncestryDNA’s website was a half-sister, Raetta, who shared the same father. When they got in touch, St Clair learned about another half-sister, Mona, who still lives in Arkansas, where St Clair was born. Earlier this month, she and Mona flew to Los Angeles to celebrate Raetta’s 80th birthday. After losing half of her identity, St Clair gained another family. And the Facebook group has given her purpose.

Recently, St Clair decided to found a nonprofit called NPE Fellowship. Members of her Facebook group had started donating DNA kits and fundraising to help each other find biological families. The community was outgrowing Facebook, St Clair realized, so again, she took action. She hopes the nonprofit can also reach people too scared to tie their real Facebook accounts to such sensitive revelations.

Back in 2016, when she first learned about her biological father, she remembers crying in bed, asking God why it had to happen to her. She heard a voice: “My darling child, it had to happen because there are a lot of lost souls, and they need somebody who’s strong enough to help them and lead them. The only way you could do that is if you’re one of them.”

Have you taken a DNA test with unexpected results? We want to hear your story. Submit a letter to the editor or write to letters@theatlantic.com.