Born 5 January 1921 Crown Prince Jean was the first male heir to the throne to be born on Luxembourg soil since the 13th century.

On 5 January 1939 he came of age and received the title of Crown Prince of Luxembourg in his capacity as Heir Apparent to the Crown of the Grand Duchy.

From 1940 to 1942 he was in exile in Canada with his family. In Quebec he studied law and political science at Laval University.

Between 1941 and 1942 he participated in  goodwill  tours in the United States of America and Brazil to meet the Luxembourgish diaspora.

In October 1942 he joined the Irish Guards as a volunteer in the British army. His training ended at the Royal Military Academy Sandhurst, England on 28 July 1943 with the rank of Second Lieutenant. He then joined the 3rd Battalion Irish Guards  of the Guards Armoured Division.

On 11 June 1944 with a small group of soldiers he landed in Normandy ahead of his unit. He subsequently served in the 32nd Brigade of the Guards Armoured Division taking part in the Battle of Caen. Moving northeast he crossed the Seine on 25 August and reached Brussels on the evening of 3 September. On 10 September in the afternoon, a few hours after his father, he joined the American troops that had liberated Luxembourg city. The two princes were greeted by the population with great enthusiasm.

A few days later he joined his unit who engaged in the ‘Operation Market Garden’ (liberation of Arnhem). During the ’Battle of the Bulge‘, the Guards armoured Division was to block the German advance to Antwerp between Namur and Tienen. On 11 February 1945 the 32nd Brigade attacked the Siegfried Line in the Reichswald, south of Nijmegen. After the capture of the Reichswald they moved towards Bremen and Hamburg.

In early April, Prince Jean was ordered to Luxembourg city where the return of Grand Duchess Charlotte was expected. On 14 April 1945 he witnessed the triumphant return of his mother.