My child has never known their father, a man I had a one-night stand with. I've just learned something horrific about him.

Care and Feeding is Slate’s parenting advice column. Have a question for Care and Feeding? Submit it here .

Seven years ago, I got pregnant from a one-night stand. I decided to keep the baby, because for years, doctors told me that I would not be able to have one. The man I was with had no desire to be a part of our child’s life, and I had no problem with that. Recently, I decided to track him down; I wanted my child to have some knowledge of his medical history. I was completely thrown by what I found out.

He is currently incarcerated for a horrific sexual assault on a minor. Needless to say, I am incredibly relieved that I never involved him in my child’s life. But what do I tell them when they inevitably ask about their father?

—Sometimes the Past Is Best Left Alone

Dear S