Also, historians have basically come to the conclusion that he did it for shits and giggles. Like really.
"The Chevalier d’Eon was a French soldier, diplomat and transvestite, who was declared to be a woman in 1777. D’Eon lived in Britain from 1762 as a man and from 1785 as a woman during which he was renowned for his public fencing demonstrations. He fought wearing a black dress like this one and his Croix de Saint Louis, awarded for diplomatic achievements on behalf of the French King. His cockade shows his support for the new French Revolutionary government who he wrote to, in 1792, offering to lead an army of women against France’s enemies.”
Portrait of Don Luis de la Cerda, later 9th Duke of Medinaceli by Ferdinand Voet, 1684
Anton Raphael Mengs:
Portrait of Maria Luisa of Parma as Princess of Asturias, 1766. (detail)