Prince Sixtus of Bourbon-Parma, photo around 1910
Sixtus Affair: Xaver and Sixtus von Bourbon-Parma, brothers of Empress Zita, served as officers in the Belgian army and acted as mediators in secret peace negotiations between Austria and France from February through April 1917. In two letters addressed to Prince Sixtus (1886-1934) dating from March 24, 1917 and May 9, 1917, Emperor Karl I recognised France´s claim to Alsace-Lorraine. However, when Italy claimed South Tyrol, the peace negotiations failed. Provoked by a speech of the Austrian Foreign Minister O. Czernin, the French Prime Minister G. B. Clemenceau published Emperor Karl´s letter of March 24, 1917 on April 12, 1918, thus seriously straining Austria´s relationship with Germany. Czernin, who had not been informed about the letter, resigned from office after a dispute with the emperor.
Literature: R. A. Kann, Die Sixtus-Affäre und die geheimen Friedensverhandlungen Österreich-Ungarns im 1. Weltkrieg, 1966.