Father of 3 children turns out to have been infertile all his life.

Not his father 

Richard didn’t circle around it. “One of the things the doctor told me was that someone with this disease cannot have children,” he said. His son looked straight at him, then cut him off: “So what you’re saying, dad, is you’re probably not my father?” 

Richard burst into tears. It took a while before he could continue the conversation.