Maybe he had siblings or cousins?
Maybe it’s through a sister, since he has a sister in modern times. She could’ve been married off or something during this point of the story
He does have a wife though I believe they never got to spend a night together.
I believe the woman he ran into while at the palace was his sister. A half sister but still a sister.
Or reincarnation. So it’s the same soul that got reborn rather than a descendant. Would also explain why he got the flashback in the first place? (Uke’s the one having a flashback right? This arc’s so long it’s been a while lol)
spoiler
It was mentioned that as long as Hyoun wished for it. He would be reincarnated. However he thought it would be for the best that Taehyuk to be reborn as a descendant of someone who looks similar to him aka his sister. That's why he spared all of those people after Taehyuk died.
Spoiler
The king disappeared(presumed suicide), the eunuch was punished and the dragon caused calamity then he saw the sister which resembles his beloved. The sister told storied of his brother to the dragon and also ask someone to paint the dragon with the hopes that the brother would see it in the future. The dragon left after the princess child became the ruler and he continues to wait for his lover to be reborn.
I'm just wondering how did they become descendants of the lover when he didn't have any babies or does he?