The Lieutenant-representative (French: lieutenant-représentant) in Luxembourg is the title borne by the heir apparent to the throne during a period in which the reigning grand duke formally retains the throne but delegates to their heir the exercise of most constitutional powers to prepare them for their accession to the throne. This practice has been customary since the reign of Grand Duchess Charlotte.
Despite the lieutenant-representative's history as the title borne by the heir to the throne as they exercise the monarch's duties in preparation for the throne, Chapter I, Articles 6-8 of the Constitution of Luxembourg stipulates that a regent may be appointed in the event the reigning Grand Duke is a minor or is incapacitated.
Hereditary Grand Duke Jean was appointed lieutenant-representative on 4 May 1961 and exercised the functions of head of state during the final years of the reign of his mother, Grand Duchess Charlotte, until her abdication on 12 November 1964, when he succeeded as Grand Duke.
Hereditary Grand Duke Henri was appointed lieutenant-representative on 4 March 1998 and carried out the duties of the crown until the abdication of his father, Grand Duke Jean, on 7 October 2000, upon which he succeeded as Grand Duke.
Hereditary Grand Duke Guillaume was appointed lieutenant-representative on 8 October 2024 and exercised the authority of the crown until his father, Grand Duke Henri, abdicated on 3 October 2025, whereupon Guillaume acceded as Guillaume V.