Dear Prudence: My husband and I married about 25 years ago and had a daughter not long after. A few years later I had an affair with a co-worker.

My husband and I split up, I moved in with my parents and continued to see the "other" man. I got pregnant by him and we decided to be together. But I realized it was lust, not love, and told him it was not going to work out. He immediately moved across the country. We had some tense conversations about the baby and things ended on a bad note. I reconciled with my husband and delivered a healthy boy my husband has loved from the beginning.

I heard sporadically from the "other" man but he never filed for paternity and only requested a few pictures. My husband raised the baby as his own, and our son is now 20. He and my husband are so close it's amazing.

Now, the "other" man has contacted me, after all this time, and wants to meet our son. It will crush my son and destroy his trust. He will question his identity, he will hate me, and it will just be awful. My husband will be devastated. He always thought we would take this secret to our graves and our son would never know. Do I tell our son and hope he can forgive us? What do we do?

Prudence says: I wish that when your son was a little boy you and your husband had explained his unconventional paternity.

You could have told him that some people have different biological parents from the ones who are raising them — surely he had friends who were adopted or had a stepparent. You could have explained that you two would always answer any of his questions about this. You would have emphasized that his real father is, and will always will, be the man he calls Dad. Then you wouldn't have had to hope this secret could be buried along with the two of you. Nor would you have feared what is happening now, that the man who was essentially a sperm donor reappears, asserting his paternity.

I understand why you couldn't bring yourselves to tell. But you were deluded to think that a man who has been lurking around the periphery of your lives would just simply vanish. There was always a chance he'd want to see how his son turned out. Sure, you could try to convince your former lover that showing up will only cause havoc and beg him to go away. But you know you'd probably never rest easy again, wondering if this man might decide to bypass you and contact your son directly. Imagine your son coming to you and saying, "I got a bizarre e-mail yesterday from a man claiming to be my father."

So now you and your husband have to sit your son down and have a version of that long-delayed conversation outlined above, and apologize for not telling him sooner. (You will also need to inform your daughter.) Yes, his world will be roiled. But I'm betting that after all of you work through this, you will find your family still rests on the secure foundation of love you've all built.