"Father." Indeed, Canglong, the Second Emperor, was Huan Yi's son—born from one of the many experiments that the Demon Child carried out to challenge the curse that Yuanqi put on his bloodline and make sure he could choose whether his offspring would be born as mortals or inherit his powers.
And so, starting with the Second Emperor, all Heavenly Emperors directly descended from Huan Yi, a secret that in the current Three Realms, Huan Yi, the Immortal Venerables and a select few others, were the only people to know.
Inheriting the Heavenly Dragon blood of his mother, and the all-dominating paragon power of his father, Canglong was born with peerless martial talent, effortlessly cultivating his body and soul to the peak of the Martial Ancestor realm.
For those that forgot, Di Jun was the Tyrant Dragon Monarch, Incarnation of Majesty, and creator of the Celestial Realm.
With that said, enjoy!