Ulrich II, Count of Celje, last ruler of the County of Cilli, is assassinated in Belgrade.

Ulrich II, or Ulrich of Celje, was the last Princely Count of Celje. At the time of his death, he was captain general and de facto regent of Hungary, ban (governor) of Slavonia, Croatia and Dalmatia and feudal lord of vast areas in present-day Slovenia, Croatia, Bosnia, Austria, and Slovakia. He was also a claimant to the Bosnian throne. He was killed by agents of the Hunyadi clan under unknown circumstances, which plunged Hungary into civil unrest that was resolved a year later by the sudden death of king Ladislas the Posthumous and the election of Matthias Corvinus, the son of John Hunyadi and Ulrich's son-in-law, as king. Ulrich's possessions in the Holy Roman Empire were inherited by Emperor Frederick III, while his possessions in Hungary were reverted to the crown.

The County of Cilli was a medieval county in the territory of the present-day Slovenia. It was governed by the Counts of Cilli. Following the death of Ulrich II of Celje, the county was subsumed by neighbouring Duchy of Styria.

Belgrade is the capital and largest city of Serbia. It is located at the confluence of the Sava and Danube rivers and at the crossroads of the Pannonian Plain and the Balkan Peninsula. According to the 2022 census, the population of Belgrade city proper stands at 1,197,114, its contiguous urban area has 1,298,661 inhabitants, while population of city's administrative area totals 1,681,405 people. It is one of the major cities of Southeast Europe and the third-most populous city on the river Danube.