There is a man looking at someone's picture and says:
Brothers and Sisters I have none,
but this man's father is my father's son.
Whose picture is the man looking at?
"My Father's Son" means "Me, Myself". So by saying "This man's Father is My Father's Son", the man says that he is the Father of the person in the picture. hence the person in the picture is none other than his SON or DAUGHTER. But since he uses the word "MAN", the person in the picture is none other than his SON.