King Arthur: Bloodbound Brothers

The prophecy said: "The second-born of the royal line will bring this kingdom to ruin." So Mordred, the younger brother, was exiled to the North at birth. Arthur, the elder, took a crown that was never meant to be his alone. Ten years later, beneath a blood moon, the brothers meet again at the edge of a sword. A brutal battle. A blade through the heart. A single line: "Miss me?" But the blade didn't kill him. A dragon, asleep for a thousand years, stirs at the touch of that shared blood. An ancient curse binds their lives as one: what prospers one, prospers the other; what destroys one, destroys both. After ten years of hatred, neither can walk away. The lords of the North are sharpening their swords. The Astral Order has been pulling strings from the shadows all along. And the awakened dragon, guardian or catastrophe, no one can say. When hatred and blood live in the same body, these brothers will either drag each other into ruin, or forge a path no one else could have imagined.

Synopsis from MoreShort.