What is desiree's origin?

Desiree, the central character of the story, is a foundling discovered by Monsieur Valmont on the gateway to his estate. She is later raised by him and his wife, Madame Valmonde, who sees her as gift from God, as the couple cannot have their own children. “Monsieur Valmondé grew practical and wanted things well considered: that is, the girl’s obscure origin.