As Tim remembers it, he decided to donate sperm after reading about lesbians looking for donors in a San Francisco gay-pride magazine. How great, he thought, to help families have kids. As a young gay man in the ’80s, decades before marriage equality, he didn’t think he would otherwise have children. But he soon learned that he could not donate to a sperm bank—for the same reason he could not donate to a blood bank. Because he had sex with men, he was seen as a risk for HIV.

The controversial policy is in place even today, even though banks have long quarantined and tested sperm for HIV. It didn’t sit well with Tim, so he lied. He passed all the health screenings, began donating regularly, and for years never thought about it much. His sperm went all over the country. Unlike other donors, who provide sperm mostly for cash, he did eventually want to meet his donor kids, but he didn’t expect to—at least not until they were 18 and came looking for him on their own.

In the mid-2000s, Tim heard about the Donor Sibling Registry, and for the first time, he realized he might get to know his donor kids as kids. He signed up. He matched with a handful of the moms who had picked him as their sperm donor. Still, he says, “they all seemed really reluctant.” They had their own lives and their own families; they weren’t ready to bring in a stranger. He stopped checking the site regularly because he wasn’t getting frequent messages.

But Si’Mone Braquet and her 9-year-old son, McKay, were different. When Tim didn’t respond immediately to her message on the Donor Sibling Registry, she emailed the site’s founder, who in turn forwarded the message to Tim. He remembers her saying in their first phone call, “Your son wants to meet you.” Those words stuck him. “That’s the first and only time,” he says, “that someone who has gotten their donor sperm from me has referred to the child as mine.”

Read: The overlooked emotions of sperm donation

McKay had started asking about his dad when he was about 5. At school, he would make cards for Father’s Day, only to have no one to give them to—so he started keeping a “daddy box.” Once Si’Mone got in touch with Tim, father and son started talking for an hour every day. Tim came down to visit during his spring break. “I’m super nervous,” he recalls. “I have no idea what to expect.” McKay remembers waiting by the big window at the front of his house, scanning the street for his dad. For two strangers, even for two genetically related strangers, they hit it off. They rode bikes. They went by McKay’s school. And McKay gave Tim the daddy box.

Once the other moms saw photos of Tim with McKay on the Donor Sibling Registry, they got comfortable with the idea of their kids meeting him too. He started going to see other kids—a boy near Los Angeles, a girl near San Francisco, and so on. He also began coming out one by one to their moms. “I was super nervous about it at first because I had lied,” he says, but none of them made a huge deal about it. Once, before Tim went to visit McKay in Texas, Si’Mone’s family did bring up a photo that her family had found, of him with “cross-dressers.” He corrected her. “I was like, ‘Honey, they’re drag queens. They’re different because they have a sense of humor,” he recalls, laughing. It didn’t bother Si’Mone after that, and as the kids themselves have gotten older, they have also realized in their own time that Tim is gay.