Prince Guillaume of Luxembourg (Guillaume Marie Louis Christian; born 1 May 1963) is the third son and youngest child of Grand Duke Jean and Grand Duchess Josephine-Charlotte of Luxembourg. His godparents are Louis, Prince Napoléon and Princess Maria Cristina of Savoy-Aosta

Guillaume was born in Betzdorf Castle. He attended secondary school in Luxembourg and Switzerland, and received his baccalureate in Grenoble in 1982. He continued his studies at the University of Oxford in the United Kingdom, and later at Georgetown University in Washington, D.C., where he graduated in 1987. Prince Guillaume of Luxembourg was presented the degree Doctor of Humane Letters, honoris causa, at Sacred Heart University’s Academic Convocation and Induction of the Class of 2011 on 10 September 2007. The official ceremony welcomed the first-year students to SHU with a formal academic procession and messages from the faculty, student representatives, and president Anthony J. Cernera, PhD.

Guillaume worked for six months at the International Monetary Fund in Washington, and spent two years working for the Commission of the European Communities in Brussels. He is currently a director of ArcelorMittal.

Guillaume married Sibilla Sandra Weiller, a daughter of Paul-Annik Weiller and of the Italian princess Donna Olimpia Torlonia di Civitella-Cesi (daughter of the Spanish Infanta Beatriz of Spain) civilly on 8 September 1994 and religiously in Versailles on 24 September 1994, who received the title “Princess of Luxembourg”. Guillaume and Sibilla have four children:

Prince Paul Louis Jean Marie Guillaume of Nassau (b. Luxembourg, 4 March 1998) Paul Louis is godson of his cousin, Hereditary Grand Duke Guillaume of Luxembourg.
Prince Léopold Guillaume Marie Joseph of Nassau (b. Luxembourg, 2 May 2000).
Princess Charlotte Wilhelmine Maria da Gloria of Nassau (b. Luxembourg, 2 May 2000).
Prince Jean André Guillaume Marie Gabriel Marc d’Aviano of Nassau (b. Luxembourg, 13 July 2004).
Their sons are in the line of succession to the throne of Luxembourg.

Prince Guillaume is the godfather of his nephew Guillaume, Hereditary Grand Duke of Luxembourg. He is also one of the godparents of Prince Achileas-Andreas of Greece and Denmark, second son of Crown Prince of Greece.