An English monarch abdicated the throne for the first time in history on this day in 1936, when King Edward VIII faced unprecedented public backlash for his marriage to Wallis Warfield Simpson, who was both an American and a divorcee. Edward had met Simpson a couple of years prior while hobnobbing with the fashionable and rich around London and fell in love with her fast, something the royal family was less than keen on. Then, King George V died, and it was Edward's turn to rule.
The new king was well-liked, but the social elites who knew about the affair were greatly displeased. Adding to the controversy of her being American and divorced was that Simpson was still married to her second husband. When Edward began pressing Parliament to permit him to marry Simpson, the scandal broke into the public eye. British politicians, the Church of England, and others made their displeasure heard. The king abdicated and his younger brother, now George VI, donned the crown. The next year, Edward, now the duke of Windsor, and Simpson married.
You can read more about Edward's abdication at the BBC.