Let's analyze the statement step-by-step: Lata says:
“He is the son of the only son of my grandfather.”

Breaking it down:

• My grandfather : Lata's grandfather.
• The only son of my grandfather : This means the only son of Lata's grandfather is Lata's father (assuming traditional family structure).
• The son of the only son of my grandfather : This means the son of Lata's father.

Conclusion:

The man in the photograph is the son of Lata's father , which makes him Lata's brother.

Final answer:

The man in the photograph is Lata's brother.