Archduke Franz Ferdinand was the heir to the throne of the Austro-Hungarian Empire.

On June 28, 1914, he and his wife, Sophie, were visiting Sarajevo, the capital of the Austro-Hungarian province of Bosnia.

The visit was controversial as the date was a major Serbian national holiday, and many Serbs in Bosnia resented Austro-Hungarian rule.

The assassination was planned by a Serbian nationalist secret society known as the 'Black Hand.'

The assassin was a 19-year-old Bosnian Serb named Gavrilo Princip.

An earlier assassination attempt on the same day with a bomb had failed.

By a remarkable coincidence, the Archduke's car took a wrong turn and stopped right in front of Princip, who then shot and killed both Franz Ferdinand and his wife.

Austria-Hungary blamed the Serbian government for the assassination.

This event triggered the 'July Crisis,' a month-long diplomatic cascade that led to the outbreak of World War I.

The assassination is considered the immediate trigger, or 'spark,' of the war.