Throughout history, people related by blood and/or marriage were super close - sometimes too close. There are tons of historical examples of genetic mutations resulting from inbreeding and even examples of incest leading to murder, but what about precedents of historical figures killed for incest?
A number of figures throughout history were executed for (allegedly) inbreeding, often a capital crime in the Renaissance and early modern periods. Who were these practitioners of historical incest? They supposedly include Henry VIII's second wife, Anne Boleyn, alleged Scottish witches and warlocks, and mother-killer Henry Learned Foote; it's a motley crew, to be sure.
By 1536, King Henry VIII's infamous second wife, Queen Anne Boleyn, had not yet delivered the son she had promised her husband. Henry had two daughters - disinherited Mary by his first wife, and Anne's Elizabeth - but ardently wanted a male heir. Besides, he fell in love with pretty, young Jane Seymour, whom he wanted to marry. So he filed a bunch of charges against Anne, including adultery and incest, so he'd be free to marry again.
Anne allegedly slept with her brother and confidant, George, Lord Rochford. The evidence at the trial was largely hearsay, leading most historians to believe she was innocent of most of the charges against her. But was the case of incest true? Probably not, though some scholars believe one of Anne's ladies-in-waiting confessed that she and George did the deed in an effort to get a royal heir. Either way, Anne was executed on May 19, 1536.
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Queen Anne's brother, George Boleyn, allegedly got busy with his sister, for which he was executed on May 17, 1536, along with her other supposed lovers. Who told the king about their "affair?" Possibly Anne's sister-in-law and George's wife, Jane Parker, Lady Rochford. She testified against them both, claiming they had an affair, which was the damning evidence the court needed to pass their death sentences.
George maintained his innocence until his death. His dying speech allegedly began as follows:
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"Christian men, I am born under the law, and judged under the law, and die under the law, and the law hath condemned me. Masters all, I am not come hither for to preach, but for to die, for I have deserved to die if I had twenty lives, more shamefully than can be devised, for I am a wretched sinner, and I have sinned shamefully."
Ugo d'Este And Parasina Malatesta, 1425
For much of history, sex between people related by marriage was counted as incest by certain religious institutions. Such was the case with Ugo d'Este, illegitimate son of Niccolo III, Marquis of Ferrara, and Niccolo's pretty wife, Parasina Malatesta. The affair became famous thanks to a poem penned by Lord Byron, but the fallout was real.
But did Ugo and Parasina really have an affair? Niccolo was notoriously nasty, and he might have wanted to off his wife to wed another à la Henry VIII. Perhaps the accusation of adultery rid him of two birds with one evil stone: a pesky secret love child hankering for more of the inheritance and a wife he no longer desired. Either way, Niccolo beheaded them both in 1425.
Thomas Weir, 1670
Usually, churchmen accused witches against the witches' will, but one man came forward and confessed to witchcraft willingly. The Edinburgh-based Major Thomas Weir wasn't your average witch - he dressed all in black and was a practicing Presbyterian - but one day while in church he suddenly accused himself of being in league with the Devil. No one wanted to prosecute him, but Weir also confessed to an affair with his sister, who corroborated his account.
He carried a bewitched staff, a gift from the Devil, and supposedly got his powers from his mother, who was a witch herself. The authorities had to convict them both, executing them in 1570. No one knows why he and his sister confessed to witchcraft and incest, but his house is still considered haunted centuries later.