If Aarti is the only daughter of Prince’s wife’s mother’s husband. Then, how is Aarti related to Prince’s son?

Mother

Explanation:

Note:

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

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

   —   ⇒ single line shown "relation between them other than Husband & Wife".

‘+’ means Men’s category

‘–’ means Women’s category

As Aarti is only daughter. So, Aarti must be wife of Prince.

So, Aarti is mother of Prince’s son.