Question

how to deal with anew person

Answer 1

You must ignore  this  person
It can be  a great  problem
if you don't  know him personally  you can't speak with him  about his sister.

Answer 2

It's gonna be a trouble if you speak to him , you have to ignore the situation 'cause you don't know the person , he may not believe you and if he did ... Don't tell him anything about his sister ..