A man is looking at a picture of a man on the wall and states: Brothers and sisters I have none, but this man's father is my father's son. Who is the man in the picture in relation to the man looking at the picture?

The man in the picture is his son. Since he doesn't have any brothers or sisters, the statement my father's son is himself. A shortened version would be this man's father is myself, so he is the father of the man in the picture.

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