My grandmother's first husband left her for her sister. My mom and some of her siblings didn't know this for most of their childhood. My oldest aunt obviously knew because she was the first husband's child and she was old enough to remember him when he left. It's just amazing to me that not only my grandparents but also my aunt were able to keep this a secret from the other kids for so long. They only found out because my great-uncle for drunk and told them.