Ex & Family

So I've recently noticed that one of my exes (from 2001, who was also my 1st EVERYTHING) has been frequently tlkn with my niece on fb. Yesterday I found out that he was at her house too. Knowing the type of person she is, I'm almost sure they're talking/sleeping together. I'm not sure if she knows/remember that he & I used to date, but im positive thatbhe knows she is my niece. Yea it's been many years ago & I have no feelings or anything for him, but should I still say something to them about it or at least to my niece?