How else do you protect your amazing and brilliant genetics? The royals of Europe all practiced incest. Being rich and powerful and bored leads to some weird fetishes.

His sister's diary shed some light onto that. A sick household environment to be sure.

"Smashing her vagina while listening to her parents fucking"
"Inappropriate showers with her dad"
"Knows she was molested" and her memory fuzzy around the molestation events (common trauma response)

What a bunch of monsters.

I remember reading something about his first wife saying "joes a monster" and trying to keep their young daughter away from him..

Incest is all relative.