 Mirko lost his chance to succeed to the Serbian throne in 1903, due to the assassination of Alexander and Draga and the resulting conferral of the crown upon Peter Karađorđević, his brother-in-law.However, in 1911 he joined the Black Hand "Unity or Death" secret society which sought the unification of all Serbs in the Balkans, especially those under Austria-Hungary, and was determined to become the society's unified leader.Mirko divorced his wife in 1917 and moved from Paris to Vienna, where he died in 1918.