Grand Duke's Official Birthday

The Grand Duke's Official Birthday (Luxembourgish: Groussherzogsgebuertsdag, French: Célébration publique de l'anniversaire du souverain), also known as Luxembourgish National Day (Luxembourgish: Lëtzebuerger Nationalfeierdag, French: Fête nationale luxembourgeoise, German: Luxemburgischer Nationalfeiertag), is celebrated as the annual national holiday of Luxembourg. It is celebrated on 23 June, although this has never been the actual birthday of any ruler of Luxembourg.

Source: Wikipedia — Grand Duke's Official Birthday (CC BY-SA 4.0)