Illegal love
Finding out that your father and mother were actually an illegal teacher and student relationship can be a huge bomb to discover. Not only are you finding out that your father is technically a pedophile but that he was in a romantic relationship with a student he taught. That can be rough.
They managed to beat the system and move away before anyone caught them and they made it all legal, so there is nothing anyone can do about it. But it does leave a bitter taste in our mouths and we can’t imagine how their child feels about this new information that has come to light.