Prince Sixtus of Bourbon-Parma
|Prince Sixtus around 1930|
|Spouse||Hedwig de la Rochefoucauld|
|Sixtus Ferdinand Maria Ignazio Alfred Robert|
|Father||Robert I, Duke of Parma|
|Mother||Infanta Maria Antonia of Portugal|
1 August 1886|
Wartegg, Canton of St. Gallen, Switzerland
|Died||14 March 1934
Prince Sixtus of Bourbon-Parma (given names: Sixtus Ferdinand Maria Ignazio Alfred Robert; Wartegg, Canton of St. Gallen, Switzerland, August 1, 1886 – Paris, March 14, 1934) was a Prince of the Duchy of Parma, a Belgian officer in the First World War, and the central figure in the Sixtus Affair.
On March 14, 1919 Sixtus married in Paris Hedwige de La Rochefoucauld (1896–1986), daughter of Armand de La Rochefoucauld, Duke of Doudeauville, and his wife Princess Louise Radziwill. On the occasion of their marriage, the family acquired the Bourbon-Parma tiara from Chaumet. 
They had one daughter, princess Isabella Marie Antoinette Louise Hedwig (1922-2014), who in 1943 married Count Roger Alexander Lucien de la Rochefoucauld (1915–1970, murdered), son of Count Pierre Paul (1887–1970) and his wife Henriette Marguerite Marie de la Roche (1892–1980).
During World War I Sixtus and his brother Xavier enlisted in the Belgian Army. Several of their older brothers were officers in the Austrian Army. His sister Zita married Archduke Charles of Austria, who became the Austrian Emperor on November 21, 1916.
In 1917, Emperor Charles I secretly entered into peace negotiations with France, with his brother-in-law Sixtus as intermediary, without the knowledge of his ally Germany. When news of the overture leaked in April 1918, Charles I denied involvement until the French prime minister Georges Clemenceau published letters signed by him. This led to an even more dependent position of Austria with respect to its German ally. This is known as the Sixtus Affair.
- In Nordostarabien und Südmesopotamien: Vorbericht über die Forschungsreise 1912, with Alois Musil (Vienna: 1913).
- Le Traité d'Utrecht et les lois fondamentales du royaume (Paris: E. Champion, 1914). Reprinted (Paris: Communication & Tradition, 1998).
- L'offre de paix séparée de l'Autriche, 5 décembre 1916 - 12 octobre 1917 (Paris: Plon, 1920). English translation: Austria's Peace Offer, 1916-1917 (London: Constable, 1921).
- La dernière conquête du roi Alger, 1830 (Paris: Calmann-Lévy, 1930).
The television series The Young Indiana Jones Chronicles presents Sixtus (played by Benedict Taylor) and his brother Xavier (played by Matthew Wait) as Belgian officers in World War I who help the young Indiana Jones. Sixtus and his brother Xavier and the Sixtus Affair are the central subjects of the historical fiction novel "Kingdoms Fall - The Laxenburg Message" by Edward Parr.