On Sunday, Grand Duke Henri made the surprise announcement to step back from his duties and pass on his duties to his son, the Hereditary Grand Duke Guillaume, paving the way for his abdication.

Article 42 in the the Luxembourgish Constitution stipulates that the Grand Duke can be represented by a 'prince of the blood' and can act under the title of 'Lieutenant of the Grand Duke' and must reside within the Grand Duchy.

The historian Jean-Marie Majerus notes in an interview with RTL that the definition of a lieutenancy has changed from its original 19th century interpretation. For instance, Prince Henry of the Netherlands governed the Province of Luxembourg via lieutenancy from his brother King William III of the Netherlands.

Since the 20th century, however, a lieutenancy signals an imminent royal succession, according to Majerus.

Questions remain on what duties the Hereditary Grand Duke will be taking over from his father, the Grand Duke in October as Lieutenant-Representative. Majerus states that "the Grand Duke can pass on whatever duties he pleases. The Constitution does not contain any indications or limitations in terms of the duties the Grand Duke can or cannot pass on to his Lieutenant Representative. This can range from the Lieutenant Representative being able to receive an ambassador and complete their accreditation process, which is more of a formality, to the Lieutenant Representative being able to approve an act of legislation. So in many ways, the Lieutenant Representative can do what the Grand Duke does but the Grand Duke remains the Grand Duke until he officially abdicates.

In October, the Lieutenant Representative will take his oath and his duties must comply with the Constitution, according to the historian. The details of the ceremony taking place in autumn rests in the hands of the Grand Duke. 

"It lies with the Grand Duke to decide what kind of ceremony will take place. There aren't really any firm rules but I am expecting a formal, festive ceremony where the Hereditary Grand Duke will officially receive his duties. Before the Lieutenant Representative, who will later become the Grand Duke, officially takes over his duties, he will need to make an oath just like any government Minister when they take on their mandates."

This will be the sixth lieutenancy for Luxembourg. How long Prince Guillaume's lieutenancy will last is yet to be seen. The last two lieutenancies lasted three and a half years and two and a half years respectively.