Incest was considered a capital crime in many societies during the Renaissance and early modern period. That certainly didn't stop some historical figures from allegedly breeding with their relatives. History is littered with examples of genetic mutations caused by incest and bitter revenge plots that ended in murder.
Among the incestuous were Scottish witches and warlocks, and even some royalty. But while some denied their twisted romance ever happened, others had no shame in admitting just how close their family was.