The director of my kid's daycare friended my wife. Turns out, her fb feed had a lot of posts about her marital troubles. In the most recent one at the time, another friend of hers commented something like "is there anyone else you can talk to about this instead of posting it all over social media? How about your pastor?" To which she replied "our pastor doesn't like us after he found out how closely related we are."
That's how we learned she married her first cousin.