I was old enough to be a grandmother myself before anyone in my family informed me of our multi-generational history of father-daughter incest. The things done to my grandmother, that she kept secret until near the end of her life...! She imagined she was the only victim until she began sharing her secrets and others shared their own secrets. It explains so much. It explains why, when I told my parents some of what had been done to me, they turned away and pretended I had not spoken and left me alone in my fear and shame.
Denial is a mental illness.