French Royals Not Invited
This article dated April 28, the eve of the wedding, explains the reasons why the French royal families were not invited to the ceremony:
(…) And yet when one glances at the list of invited guests, there are no French princes. Even if they are not about to wear the crown of France, it was normal to expect that at least one of them would receive an invitation.
In the entourage of the Count of Paris, it was affirmed that he did not receive an invitation. "Nobody in the family, as far as I know, was invited. And yet, when the Prince is invited somewhere, he goes." An error on the part of the English royal family? "There is no coldness between the French and English families," continued the adviser. "I'll give you an example: Prince Charles went recently to Portugal and on that occasion, he visited Charles-Philippe d'Orléans." But "the Count of Paris, and the Duke of Vendôme, have both been invited to the marriage of Prince Albert II of Monaco."
(…) The entourage of Jean d'Orléans, Duke of Vendôme, son and heir of the Count of Paris, informs us that he did not receive an invitation. And yet the royal family had been invited to Prince Jean's marriage: "an invitation was sent to them but they answered that they would not be able to attend." Have the English forgotten their good manners? "No, the Prince was not surprised… since the whole Commonwealth was invited, he could have been invited or not. Moreover, it appears that the British Crown preferred to give priority to reigning families."
Note: I noticed that Constantine of Greece and his wife were invited. They are not reigning monarchs. He was deposed in 1973, but has been living in England.
The story is the same from Louis de Bourbon. The eldest Capetian was not part of the guest list. "He will not attend" his private secretary declared, then added that he had not been invited. "The relations between cousins have always been complex and the English monarchy has always been closer to the House of Orléans than to the Bourbons." It should be added that the English royal family had not received an invitation to the marriage of Louis de Bourbon.
The fact remains that between Sheikh Ahmad Hmoud Al-Sabah from Koweït, and the heir to the throne of Bahrein, and the Emir of Qatar, and even Prince Alexander of Yugoslavia, you could have imagined that the presence of a French prince would not have been inappropriate, especially when you recall that the ancestors of Prince William, Arthur, Philip, Louis of Windsor claimed the Crown of France and proclaimed themselves king of France until 1801. Perfidious Albion...