Stjepan Tomaš Kotromanić - Beheaded in 1463

This profile gives his death as 1461 but Wiki states that:
"... in 1463, he sent for help from the Venetians. However, none ever reached Bosnia. In 1463, Sultan Mehmed II led an army into the country. The royal city of Bobovac soon fell, leaving Stephen Tomašević to retreat to Jajce and later to Ključ. The Bosnian Kingdom was soon conquered by the Ottoman Empire. The King was captured in Ključ, and despite promises to the contrary, brought back to Jajce and beheaded on the nearby field known as Carevo Polje (Tzar's Field)."

It actually give a firm date as 5 June 1463.

Obviously Wiki isn't the best source in the world but the beheading of a King is a fairly note worthy event, as is an invasion of Europe by the Ottoman empire.