What family secret did you not know about until you became an adult?

Not really a secret but I guess it was just a bit heavy for kids. I didn’t find out until I was much older, that the two kids my grandmother raised (given to her by the church, permanent foster situation) actually came to her under some pretty terrible circumstances. I knew my “aunt” was born to an active addict, but what I didn’t know is that she and my “uncle” witnessed their mom being beaten to death when they were small. They probably don’t remember this luckily and it is never, ever discussed.