A man buried in a tomb 5,200 years ago was born from incest. Crazy, right? A team led by geneticists Lara Cassidy, and Daniel Bradly had DNA extracted from the skeleton, and found that it displayed an unusually high number of identical versions of the same gene. This particular pattern indicated that the parents were either siblings, or parent and child.
Cassidy and Bradly's team studied DNA from 44 other individuals buried around in various Irish tombs and graves dating between 6,000 and 4,000 years ago. The only indication of inherited genetic markers of incest was found in the 5,200 man.
Although incest is socially prohibited, it was once widely favored in instances of royal inbreeding. The famous King Tut is also a product of royal inbreeding.
2nd Link: https://www.nationalgeographic.org/encyclopedia/king-tut/