
King's Heart weakened his dragon power and basically manipulating him until his last breath. There's no clear mention about his last moment but his corpse...uhmm spoiler ahead,
Again SPOILER and another WARNING for unsettling story ahead :
That darn Truyde ate his corpse to absorb his power into him and neutralizing potion.This method has been in place since generations. Meaning his ancestors also ate The Kings's corpses. This is part of Truyde's family big secret.
Another spoiler :
There will be act of gore and cannibalism. I was genuinely surprise why the author had to make a sudden turn like this. It was shocking and unnecessary at all. It stained the story badly. I don't know if this manhwa/webtoon version will stick to its original story or not, but be aware.

Truyde's family do the nastiest things to spread their influence in the palace and controlling the Kings for generations. Even when Kings's bodies lies 6th under ground, they still plotting to consume their power.
Karas is not an angel either. He is like an explosive nuclear bomb and glad that he has Regas & his knights on his side who able to direct his temper most of times. It's like a war between evil vs lesser evil tbh. We have not seen what Karas capable of doing yet, but he actually do everything, right or wrong to defeat King's Heart behind the scene. One thing for sure, he can be too extreme, same as Truyde.
So, i let this marinate for a long time—i'm now just rereading the whole manwha and i just realized, where did the previous King go? Was he killed or was he just..wiped from the story?