If Krishna says, "Shaan’s mother is the only daughter of my mother", how is Krishna related to Shaan?

Uncle

↑ 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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ATQ,

The 3rd option is satisfying the equation.

Therefore, 3rd option is correct.