Introducing a boy, Leela said to Ana, "He is the only son of the only child of my grandparents." How is the boy related to Leela?

Brother

↑ or ↓ ⇒ Upward or downward line shown "generation gap".

   =    ⇒ Double lines shown "relation b/w Husband & Wife"

   —   ⇒ single line shown "relation in same generation other than Husband & Wife".

   +   ⇒ Plus sign shown " Male".

   -   ⇒ Plus sign shown " Female".

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Hence, that boy is brother of Leela.