Royal Marriage Between the (Secret) Futa Princess and Another Princess

It had been arranged years ago, now that both princesses were old enough (teens, exact ages can be discussed), it was time to make it official. It had been the talk of both kingdoms for ages, and a matter of confusion for everyone outside of one of the royal families. For two princesses to be married to each other, for two women to marry each other, it was unheard of. The one king had no sons, so it was very confusing when he offered a marriage proposal for his eldest daughter to a younger daughter of a neighboring kingdom. Did he just want an alliance? Either way, he offered a great deal of gold, enough for his neighbor to agree to a seeming pointless novelty of a marriage.

The secret, unknown even to the other princess, was that this ’princess’ was a futa. She could not be considered a son, or a man, but if given a wife, she could father children. This is a world where she is not the first futa but they are rare enough to essentially be myth/legend, and many doubt they could actually exist.

I want to explore such a story, exploring gender roles, sex, society, among other things for such a couple. A proper royal marriage too, there will be no love at the start, though there is a chance one or both could develop feelings for the other. We would start with the other princess arriving and their marriage, the other princess discovering the truth about her wife that night, for their first time in bed together.