Riddle: There was a man who has been in prison for 20 year. In these past 20 years he has never had a visitor. One day, after his 20th year in prison, a man came to see him. The guard was very surprised and curious of the vistor, after all these 20 years no one ever came to see him. So the guard goes to the prisoner and asks him, who is this man that came to see you? The prisoner replies:
"Brothers and sisters,I have none.
That man's father is my father's son."
Who is the visitor to the prisoner?