Errol Musk, father of Elon Musk, had a baby with his step daughter who he had known since she was 4 months old.

Elon Musk apparently hates him and in his own words: "You have no idea about how bad. Almost every crime you can possibly think of, he (Errol Musk) has done. Almost every evil thing you could possibly think of, he has done."

https://www.telegraph.co.uk/news/2018/03/25/elon-musks-father-has-baby-step-daughter-has-known-since-four/