Lookalike
I had an on-and-off fling with a girl when we were 18 and 19. She got pregnant and had a son while I was away studying. When I came back into town, people congratulated me when they met me on the road. They kept telling me how much he looks like me. I told her I would be there for them if I were the father, but I had to have some blood taken for DNA testing.
The results were rather surprising—it turns out the father was another guy who looks very much like me. Story credit: Reddit