The Sixtus Affair (German: Sixtus-Affäre, Hungarian: Sixtus-ügy) was a failed attempt by Emperor Charles I of Austria to conclude a negotiated peace with the allies in World War I.
[1] In 1917 the war was dragging on towards its fourth year, and Charles decided to secretly enter into peace negotiations with France.
He used his brother-in-law, Prince Sixtus of Bourbon-Parma, an officer in the Belgian army, as intermediary as well as enlisting the help of his loyal childhood friend and aide-de-camp Tamás Erdődy.
Another intermediary was Jozef Retinger, a London-based Polish literary scholar and budding politician who was a friend of Sixtus, Xavier and Zita of Bourbon-Parma and who had received backing from the British to support the initiative.
For his role as a peacemaker during 1917–1918, Emperor Charles I of Austria was solemnly declared blessed in a Mass of Beatification on 3 October 2004 by Pope John Paul II.