Found out my 13 year old has a finsta account

Just found out through my niece that my son has a secret Instagram account with a different name where he's posting stuff he'd never show us. Nothing terrible from what I can see but I'm upset he felt like he needed to hide it. Do I confront him? Do I monitor it? How much privacy should a 13 year old actually have? This parenting thing is getting harder the older they get.