Grand Duke Henri announced his abdication last year, with his eldest son, Hereditary Grand Duke Guillaume, set to succeed him on October 3. As the country prepares for the ceremonial transfer of power, the question has resurfaced for many: why a Grand Duke, and not a King? So, William I of the Netherlands became Grand Duke of Luxembourg.”Anwar Hussein // Getty Images Grand Duke Jean and Grand Duchess Joséphine-Charlotte host Queen Elizabeth and Prince Philip during a royal visit in 1976. The formal role of the Grand DukeUK Press // Getty Images Grand Duke Henri and his wife Maria Teresa on the day of his accession in 2000, with his parents, Grand Duke Jean and Grand Duchess Josephine Charlotte. Patrick van Katwijk // Getty Images The Grand Duchess and Grand Duke with their son, Hereditary Grand Duke Guillaume and his wife Stéphanie.