Crown Prince Rudolf, the only son of Emperor Franz Joseph I and Empress Elisabeth of Austria, was born on 21 August 1858. In 1889, he died in a alleged suicide pact with his mistress, Baroness Mary Vetsera at the Mayerling hunting lodge. His death had a devastating effect on the already compromised marriage of the Imperial couple and interrupted the security inherent in the immediate line of Habsburg dynastic succession. As Rudolf had no sons, his cousin Archduke Franz Ferdinand eventually became the heir presumptive to the Austro-Hungarian throne. The assassination of Franz Ferdinand lead to Austria-Hungary’s declaration of war against Serbia, starting World War I.