I dont know if anyone notice, but UDK backstory from one of his elites told is that he's been living for at least 600 year ago which is where the first "dragon" appear, and we can see on scene potrayed where he standing in front of the grave of his disciple(?) he apparently using the same circlet that dragon use, and one of the requirement for you to be reincarnated as a dragon is that you need to die agonizing death on your previous life, which we can say killed & betrayed by your own son fit the requirement.
The only plot hole i've seen from this conclusion of mine is that why his father suddenly becomes good person on his second life (at least until himzeld founded) because from the himzeld arc it is told that the first dragon and founder of himzeld can be described as perfect being, personality wise and power wise.