Until 1907, it was illegal in the UK for a man to marry his late wife’s sister (sister in law).
(The law dated back to the English Marriage Act of 1537, passed in the reign of Henry VIII of all people. Rooted in the Book of Levicitus, Chapter 18, the law prohibited marriage between relatives and relatives by marriage in situations when the first marriage had been consummated.
But the reason for overturning this archaic law was not due to sudden enlightenment, the justification for the 1907 Act was that a man of moderate means should be entitled to marry his dead wife’s sister, where that sister had come into his home to rear his children on account of his inability to pay for domestic help!
The whole thing was debated for years, as the transcript of one debate in parliament in the 1870’s about possibly repealing it attests, one of the members said marriage to a deceased wife’s sister, was a jolly good thing, because it removed the otherwise dire necessity of two mothers in law’. Good to know the ‘mother in law’ joke was alive and well in Victorian England!
“Nature must obey necessity.” William Shakespeare.)