Idk if we ever get the lore behind Cintra refusing to have a mage (they have a druid but their views on magic differ by a lot) and I like this au too much to keep it collecting dust in my docs, so here is a tentative plan for the Cintran Royal Desmond au that was inspired by a lovely review from my Letho/Desmond fic Desmond the king's bastard son. He is a few months younger than Calanthe and favored because the Mage in charge wants a puppet king. The mother's of both kids have had accidents leaving the Mage in charge. Going along with Minerva's plan, then Juno's plan left Desmond tired. So he does what he wants because this isn't his world and there are monsters to go see. The racism he discovers isn't surprising, just disappointing.
IF his half sister can agree with him, he will ensure she sits on the throne. Calanthe is suspicious, but she is aware of how much his existence is a threat. She thinks he is weak with his elf loving ways but agrees to protect them and make an example of those who would willingly attack them.
Desmond holds up his side making sure Calanthe sits with him in his king training classes. The mage is pissed but can't do anything since Desmond refuses to cooperate if Calanthe isn't involved. Even worse, he flirts with the stable boys and knights so the mage is annoyed that people are already comparing Calanthe and Desmond when there should never have been a comparison since there is only 1 heir.
When Calanthes betrothal is announced Desmond tells the mage he sister will not be going to Ebbing. Should they push the matter, they will find Cintra without any heirs as one has been shipped out and the other will never be seen again. The glow of his eyes makes the mage not call his bluff and the king from Ebbing is brought to Cintra instead.
The mage tries to push for Desmond's spouse considering the rumors about and Desmond waves them off. He wants to ensure his sister is living well before he decides anything. Should they insist then the line will end with him if Calanthe doesn't have any kids. The mage did such a great job picking her spouse and all despite Desmond disagreeing with everything about him.
The king has been bedridden this whole time, and it seems like the worst is about to happen. The mage prepares for a coronation suspiciously quickly. The invite they grab is vague of course and that works for everyone.
The night before Desmond sneaks into the mage's room and uses his apple powers to lock their chaos. He detours to the room holding the ceremonial armor commissioned for him and bam, it's Calanthe sized now. The massively sized portrait at the entrance is also changed from Desmond to Calanthe with a snap of his fingers.
They next day the castle is too busy with the coronation preparations to focus on Desmond. The mage doesn't notice anything since they ask about the preparations 'the are going well' if Calanthe had anything to say 'no she is being dressed as you requested' so when the Coronation is in full swing, they falter when the person in the well fitted armor is Calanthe.
They can't back out. It's too late to do anything so they continue the coronation while plotting to kill Calanthe later. An accident or 3 just to be sure. Instead, the mage gets beheaded after the crimes are listed out. Most shocking of all to the people is the fact that the mage doesn't user their magic. They see this as a sign of Calanthe's right to rule.
Her knights, because Desmond trained them to be loyal to her, chant Long Live the Lioness of Cintra and they do the sword arch Desmond had them practice in secret. Mentally she is embarrassed by her dramatic brother but pleased with his gift.
Maybe leave it at that and make it have hopeful open ending, but I might also plan a sequel where it's Desmond fucking with fate and keeping Duny away lol. Calanthe can say her brother ran off with the circus, a cat witcher (Gaetan), or to be with the love of his life (Filavandrel) when he is brought up.
