House of the Dragon: Stars of the Realm.

What would happen if two souls from distinct worlds reincarnated in Westeros as twins? The good news is that at least one of them has experience... "Madness and greatness are two sides of the same coin. Every time a new Targaryen is born, the gods toss the coin into the air, and the world holds its breath to see how it will land." "It seems, stupid brother, that we will have to toss many coins to see how our fate unfolds." Disclaimer: I don't own anything except my OC, the respective rights are to the original author of the ASOIAF franchise and HBO.