Guillaume 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.

[1] On the night of 10 to 11 September 2000, Prince Guillaume and Princess Sibilla were involved in a serious car accident near Paris.

The transfer of the throne between his father Grand Duke Jean and his brother Henri was postponed from 28 September to 7 October.

12 June 1968, Neuilly-sur-Seine, France), the second child of French industrialist and patron of the Arts Paul-Annik Weiller (son of Paul-Louis Weiller and Aliki, Lady Russell) and Italian noblewoman Donna Olimpia Torlonia di Civitella-Cesi (daughter of Alessandro Torlonia, 5th Prince of Civitella-Cesi and Infanta Beatriz of Spain) and the second cousin of King Felipe VI of Spain[3] civilly in Sélestat on 8 September 1994 and religiously at Versailles Cathedral on 24 September 1994, who received the title "Princess of Luxembourg".

Guillaume and Sibilla have four children: Their sons are in the line of succession to the throne of Luxembourg.