The Burgundian Catholic Balthasar Gérard (born 1557) was a subject and supporter of Philip II, and regarded William of Orange as a traitor to the king and to the Catholic religion. In 1581, when Gérard learned that Philip II had declared William an outlaw and promised a reward of 25,000 crowns for his assassination, he decided to travel to the Netherlands to kill William. He served in the army of the governor of Luxembourg, Peter Ernst I von Mansfeld-Vorderort, for two years, hoping to get close to William when the armies met. This never happened, and Gérard left the army in 1584. He went to the Duke of Parma to present his plans, but the Duke was unimpressed. In May 1584, he presented himself to William as a French nobleman, and gave him the seal of the Count of Mansfelt. This seal would allow forgeries of the messages of Mansfelt to be made. William sent Gérard back to France to pass the seal on to his French allies.
Gérard returned in July, having bought two wheel-lock pistols on his return journey. On 10 July, he made an appointment with William of Orange in his home in Delft, now known as the Prinsenhof. That day, William was having dinner with his guest Rombertus van Uylenburgh. After William left the dining room and walked downstairs, van Uylenburgh heard Gérard shoot William in the chest at close range. Gérard fled immediately.
According to official records, William’s last words were:
Mon Dieu, ayez pitié de mon âme; mon Dieu, ayez pitié de ce pauvre peuple. (My God, have pity on my soul; my God, have pity on this poor people).
Gérard was caught before he could escape Delft, and was imprisoned. He was tortured before his trial on 13 July, where he was sentenced to an execution brutal even by the standards of that time. The magistrates decreed that the right hand of Gérard should be burned off with a red-hot iron, that his flesh should be torn from his bones with pincers in six different places, that he should be quartered and disembowelled alive, that his heart should be torn from his chest and flung in his face, and that, finally, his head should be cut off.
Traditionally, members of the Nassau family were buried in Breda, but as that city was under royal control when William died, he was buried in the New Church in Delft. The monument on his tomb was originally very modest, but it was replaced in 1623 by a new one, made by Hendrik de Keyser and his son Pieter. Since then, most of the members of the House of Orange-Nassau, including all Dutch monarchs, have been buried in the same church. His great-grandson William III, King of England and Scotland and Stadtholder in the Netherlands, was buried in Westminster Abbey
According to a British historian of science Lisa Jardine, he was the first head of state to be assassinated by handgun. The Scottish Regent Moray had been shot 13 years earlier, being the first recorded firearm assassination.