finding out your SO is your long lost sibling

Saw another post on here about how a gay couple found out they were biological siblings. Hypothetically, what would you do if you found out the love of your life was actually your sibling? Keeping in mind that you were never raised to know each other as siblings. Just curious! 
Edit just to clarify: i mean this is as you find out your current SO is your biological sibling, but you had no clue until this very moment. I don't mean you started a relationship with a sibling that you already know of 😂 although top comment's reaction pic is hilarious