Question

On seeing a photograph of a boy, arun said, "he is the son of the only son of my mother" how is arun related to that boy?

Answer 1

Father son relationship

Answer 2

In the sentence, Arun says "my mother" that means his mother has only one son as Arun is the only son. Which means, the son of the only son will be son of Arun. Arun is, obviously, the father of his son.