King Gustav III of Sweden was warned of assassins at his masquerade ball. He went anyway.
Gustav had powerful enemies. This was mostly because of how he came to power: when he inherited the title in 1771 it was basically leadership in name only. The actual government of Sweden was parliament and the king just a figurehead… right up until Gustav III managed to pull off what’s called a “self-coup.”
Basically, there were concerns that parliamentarians were being bought off and influenced by foreign powers such as Russia (this was, by the way, actually happening). Gathering sympathetic troops to his side, Gustav effectively invaded his own country, dissolved parliament, and had a new constitution drawn up that gave him actual power. But the movers and shakers behind parliament never forgot.
Gustav was also a big fan of the opera. He did, in fact, found the Royal Swedish Opera and commissioned several works to be performed in it. And it was his love of the opera that was his downfall.
In 1792, a group of nobles plotted to murder the Swedish king and restore the old constitution. A sympathiser sent a letter of warning to Gustav that they planned to attack at a masked ball planned at the Royal Opera House that evening:
They are greatly upset to see this not happening at the last masquerade but they rejoice at the tidings of seeing that there will be a new one today. Bandits do not like lanterns; there is nothing more serviceable for an assassination than darkness and disguise.
Gustav ignored the letter and went anyway. He was so bold as to stand openly in his box at the opera, looking out over the masked throng below and daring the assassins to strike. When no attack came, he descended into the party. One of the conspirators, Jacob Johan Anckarström, shot him in the back.
Gustav III didn’t die right away. He survived the night, but the gunshot wound became infected and he died nearly two weeks later. The assassins’ attempt to regain power for the parliament was not immediately successful – the next king, Gustav IV Adolf, was only 14 years old but reigned for 18 years until another coup restored the power of the parliament.
The regicide at the masquerade was just too dramatic to pass up: several operas have been performed about the whole sordid drama, including Verdi’s Un Ballo in Maschera. Although, this being Verdi and this being opera, he made it a lover’s tangle instead of a political assassination.