According to Luxerazzi:
…Hereditary Grand Duke Jean joined the Irish Guards as a volunteer to be able to fight in the war… On June 11, 1944, he landed in the Normandy. As part of the 32nd brigade of the Guards Armoured Division, he took part in the Battle of Caens and the Liberation of Brussels before finally crossing the Luxembourgish border…on September 10. Together with his father Prince Felix, he was greeted by the cheers of the masses and carried on the shoulders of the Luxembourgish people. Soon after, he rejoined his regiment to free other parts of Europe from Nazi rule.
To read the entire tribute on Luxerazzi, please click here.