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Basically what the title says. I was looking through the marriages of the Princes du Sang (Princes of the Blood for those who don't know) and became increasingly confused over what was accepted as equal and was was morganatic. For example, Louis Joseph, Prince de Condé married his mistress Maria Caterina Brignole, Princesse de Monaco after her husbands death. This marriage, so far as I can tell, was accepted as equal.

On the other hand, Condé's grandson the famous Duc d'Enghien married Charlotte Louise de Rohan about a month before his murder, yet this marriage is treated as though it didn't happen or was unequal. Not to mention Louis-Philippe I, Duc d'Orléans marriage to his mistress Charlotte-Jeanne Béraud de La Haye de Riou, which as also considered morganatic.

Basically what rank was acceptable for the Royal House of France to be considered equal?
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