Kamal introduce Arun as the son of 'the only brother of his father's wife'. How is Arun related to kamal?

Cousin

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Please note:

  l   ⇒ Vertical line shown "generation gap".

 =  ⇒ Double lines shown "relation of spouse" 

—  ⇒ Horizontal line shown "relation in same generation other than spouse".

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Ans :- Arun is the cousin of Kunal.