"Brothers and Sisters, I have none. But this man's Father is my Father's son."

Riddle: A man is holding a photograph of a man and says "Brothers and Sisters, I have none. But this man's Father is my Father's son."

Answer :-
We have two clues:
"Brothers and sisters have I none..."    - No Siblings"... That man's father is my father's son."  - "That man's father is me."

So that Man is My Son