Jean Pierre Clément Marie d'Orléans, Duc de Guise (September 4,1874-August 25,1940) was the son of Robert, Duke of Chartres (1840-1910), grandson of Prince Ferdinand-Philippe and great-grandson of Louis Philippe I, King of the French.

Upon the death of his cousin the Philip VIII, Count of Paris, claimant to the throne of France as Philip VIII, the Duc de Guise became, at least for his Orleanist supporters, titular king of France as Jean III. The title was disputed by members of the Spanish Anjou branch of the family, descended from Louis XIV.

In 1899, Jean d'Orléans married his 1st cousin Isabelle d'Orléans (1878-1961). Isabelle was younger sister of Philip VIII and daughter of Philip VII and Marie Isabelle d'Orléans.

They had four children:

• Isabelle de Guise, Princess of Orléans (1900 - 1983). First married to Bruno, Comte d'Harcourt in 1923 and then to Pierre Murat, Prince Murat in 1934.
• Françoise de Guise, Princess of Orléans (1902 - 1953). Married to Prince Christopher of Greece and Denmark in 1929. He was a son of George I of Greece and Olga, Queen of Greece. They were parents of Prince Michael of Greece.
• Anne de Guise, Princess of Orléans (1906 - 1986). She married Amadeo de Savoie-Aoste, 3rd Duke of Aoste in 1927).
• Henri, Comte de Paris (1908 - 1999).

Jean III died in Larache, Morocco, in 1940.