Pointing to a photograph of a boy, Aditya said, “He is the only son of my mother-in-law’s only daughter.” How is the boy related to Aditya?

Let's break down the statement made by Aditya:"My mother-in-law's only daughter" refers to Aditya's wife."The only son of my mother-in-law's only daughter" therefore means the only son of Aditya's wife.The son of Aditya's wife is Aditya's own son.Thus, the boy in the photograph is Aditya's son.