@Shotagonist You're the Type Moon expect. Is Mordred/Saber of Red a trans boy?
@BadWrongFun The reason Mordred is presented as a girl in Fate Apocrypha is that the makers didn't want a full cast of effeminate male characters, but originally the character's gender was completely up in the air. So I can lend some credit to go full circle with that theory.
@BadWrongFun I would want to point out first that the guy who went on to write Fate/Zero once hinted at that the story between Artoria and Shirou is the story of a complicated relationship of a boy becoming a girl, so the whole trans concept is very firmly established with Saber still retaining the title of King and literally having sired Mordred. It's not hard to consider Mordred a trans boy, even tho I'd have to point at the fanservicey special outfits Saber of Red has in FGO.