Catch a Dragon, Become My Wife

To save his empress, the emperor dives deep into the thousand year lake without thinking about his own safety. In the lake, he trickes a Xuan Long who was abandoned by his tribe to go to the palace, and coaxed the Xuan Long to give him his heart. As a result of the frequent courting of the emperor, the Xuan Long sincerely fell in love with him. But in the end, he was put to death by the emperor, and disappeared like ashes after giving birth to a dragon. At this moment, the emperor recovered the memories of his past life and realised that the person he killed was his lover, the one who he had been searching for for thousands of years. (Source: Kuaikan, translated)