Earlier this year, I heard from dozens of people who took a DNA test only to discover their fathers were not their biological fathers. Many of them belonged to a private Facebook support group called DNA NPE Friends—where NPE stands for “not parent expected”—that sprung up to connect the thousands of people who’ve had their identities altered by a DNA test.

There are other sides to the story, too. The creator of DNA NPE Friends, Catherine St Clair, recently created a group for the fathers. One such father is Christopher, whose real name we are withholding at his request. Earlier this year, after buying his now 15-year-old daughter an AncestryDNA test, Christopher found out that he is not her biological father. His wife had an affair. (They also have a 13-year-old son together, who is his biological child.)

Two-and-a-half weeks after the discovery, he filed for divorce. We spoke about how revelation has changed his family, what it’s like to parent a teen going through this, and the particular difficulties of talking about this as a man.