His Royal Highness Grand Duke Guillaume, Duke of Nassau and Prince of Bourbon-Parma, born on 11 November 1981, is the eldest son of Their Royal Highnesses Grand Duke Henri and Grand Duchess Maria Teresa of Luxembourg. He has four siblings: Prince Félix, Prince Louis, Princess Alexandra, and Prince Sébastien.

Prince Guillaume officially became Hereditary Grand Duke on 7 October 2000, upon his father’s accession to the throne. He was appointed Lieutenant-Représentant of His Royal Highness Grand Duke Henri on 8 October 2024. On 3 October 2025, he took the oath of office following his father’s abdication and thereby became the new Grand Duke of Luxembourg.

On 26 April 2012, Grand Duke Henri and Grand Duchess Maria Teresa announced the engagement of Hereditary Grand Duke Guillaume and Countess Stéphanie de Lannoy.

Their wedding was celebrated at Notre-Dame Cathedral in Luxembourg City on 20 October 2012, after which Countess Stéphanie became Princess of Luxembourg and Hereditary Grand Duchess. She assumed the title of Grand Duchess on 3 October 2025, when her husband ascended the throne.

Prince Guillaume began his primary education at the Lorentzweiler school in Luxembourg. He then attended the Lycée Robert Schuman in Luxembourg City before continuing his secondary studies at the age of sixteen at the Institut Le Rosey and the Collège Alpin Beausoleil in Switzerland, where he obtained his French baccalaureate in 2001. He is fluent in Luxembourgish, French, German, English and Spanish.

After studies in international politics in the United Kingdom, he continued his education in France, earning a double degree in Arts and Political Science with honours from the University of Angers in 2009.

Alongside his university studies, Prince Guillaume also undertook training to familiarise himself with the economic and political world. He completed internships at multinational companies, including Union chimique belge in 2003 and Deutsche Bank in London in 2004. In 2005, he gained experience with the Spanish branch of the ArcelorMittal steel group. That same year, Prince Guillaume came to fully appreciate the significance of his role as heir to the throne when he participated in the United Nations Millennium Conference in New York alongside the Prime Minister and the Minister for Foreign and European Affairs, aimed at eradicating extreme poverty worldwide.

A working visit to the European Commission and to the Permanent Representation of the Grand Duchy in Brussels in 2012 allowed him to deepen his knowledge of the European Union, its negotiation processes and institutional mechanisms. On this occasion, he attended meetings of the Foreign Affairs Council and the Political and Security Committee (PSC).

From 2018 to 2019, the Grand Duke pursued postgraduate studies at the Royal College of Defence Studies (RCDS) in London, where he acquired further expertise in preparation for his future responsibilities as Head of State.

Alongside his studies, the then Hereditary Grand Duke began to carry out his representative duties.

This includes promoting Luxembourg abroad as well as supporting domestic businesses and economic initiatives. In March 2001, he was appointed Honorary President of the Board of Economic Development of the Grand Duchy of Luxembourg, a body responsible for promoting and developing the national economy, now known as the Trade and Investment Board. Since 2004, he has presented the Luxembourg American Business Award in New York.

At the age of 19, he chaired his first economic missions, which took him to the Republic of Korea, Italy and the United States. He has since regularly chaired economic and financial missions to numerous countries across Europe, the Americas, Asia and Africa.

A recent highlight was the inauguration by Prince Guillaume, in 2024, of the first edition of 'NEXUS2050', Luxembourg's major technology event. The start-up sector is an area he follows closely.

Continuing a tradition dating back 50 years, the solemn ceremony for awarding master craftsman's certificates by the Chamber of Trades is presided over by a member of the Grand Ducal Family - an honour Prince Guillaume has undertaken since 2004. Since 2015, he has also presided over the Chamber of Commerce's graduation ceremony.

For 20 years, from June 2005 to October 2024, the Grand Duke was a member of the Council of State, a position he relinquished upon becoming Lieutenant-Représentant in October 2024. During his tenure, he regularly attended plenary sessions and various committees of the Council, which allowed him to deepen his understanding of the country's institutional and legislative workings and to prepare for his future role as Head of State.

Following his appointment as Hereditary Grand Duke in 2000, Prince Guillaume accompanied Grand Duke Henri and Grand Duchess Maria Teresa to numerous representative and institutional events, including National Day celebrations, New Year’s audiences granted to national authorities and a number of State and official visits.

With the commencement of his Lieutenance in October 2024, the Grand Duke also assumed from his father the responsibility of presiding over accreditation ceremonies for ambassadors, which mark the official recognition of diplomatic representatives sent by foreign states.

Grand Duke Guillaume is particularly committed to the duty of remembrance. Inspired by the stories of his grandfather, Grand Duke Jean, who landed with the Allied troops in Normandy, commemorations of the Second World War hold a special place in the heart of this dedicated history enthusiast.

Together with his wife, who is the founder and honorary president of the non-profit organisation De Mains de Maîtres, the Grand Duke actively supports Luxembourgish arts, crafts and artisanal expertise.

Alongside their economic engagements, the Grand Duke and Grand Duchess actively participate in Luxembourg’s cultural life, attending concerts, art fairs and artistic societies, as well as visiting exhibitions at the country’s various museums and cultural institutions.

Encouraged by his grandfather and father to discover and protect nature, Prince Guillaume has been a member of the Scouts since his earliest youth.

During the summer of 1997, the young Scout enthusiastically took part in a humanitarian camp in Nepal, which left him with unforgettable memories. There, he contributed to a reforestation project as well as other initiatives in support of the most disadvantaged communities.

Proudly assuming the title of Chief Scout following the death of Grand Duke Jean, who had held the position since 1945, the then Hereditary Grand Duke made his promise in October 2019 before nearly 3,000 Scouts at the municipal park in Luxembourg City - a commitment he continues honour as Grand Duke.

On the international stage, Grand Duke Guillaume is also actively involved in world Scouting.

In 2017, he joined the Board of the World Scout Foundation (WSF) and served as its President for a two-year term from September 2021 to October 2023. Upon his accession to the throne, Prince Guillaume stepped down from his active role on the WSF Board and assumes the position of Honorary President of the Foundation the following year, a role conferred by His Majesty King Carl Gustaf of Sweden.

Grand Duke Guillaume also enjoys music, both classical and contemporary, and has a particular passion for the guitar. As a child, he was a member of the Pueri Cantores choir in Luxembourg.

He has a general interest in sports and actively participates in tennis, skiing, swimming and other aquatic sports.

Following the example of Grand Duke Jean and his father, Grand Duke Henri, Grand Duke Guillaume enjoys spending time in nature. Inspired by the stories his grandfather told him, he explored the lush forests surrounding Fischbach Castle. Today, the Grand Duke and Grand Duchess continue this tradition, spending time outdoors with their sons, Prince Charles and Prince François, whom they hope to instil with a love of nature.