Blood Covenant

After a war defeat, Cecil—the fake vampire prince swapped at birth with a heart ailment—is betrayed by his lover Rain and the true prince Leon, then cast down as a slave. On a snowy night he stumbles upon Cain, the human emperor, and discovers intimate touch heals his heart. Cain shields Cecil; they strike a bargain. Leon's schemes backfire; stripped of rank, he falls. Cain dissolves his engagement; Cecil, restored to his princely identity, marries Cain. The two stay together for good.