General

Lets say one day

You came home from school/work to find your parents sitting down at the dinner table waiting for you.
Your dad tells you to sit down beside him, as he pulls up the chair next to him. Your mom looks you in the eye and tells you what are your thoughts on incest?
(Regardless your reply here, though I'd like to know.)
With the most serious expression, your dad tells you that he & your mother are brother & sister.
How do you react?

Note: Even if your parents aren't together, let's just say one of them are telling you this then.