Izyda:
What if Jang Uk is not the son of the previous ruler? Or maybe the letter that Jang Kang received was fake and the king never spent the night with Jang Uk's mother? Crazy theory: How about the theory that the deceased king had a daughter and not a son? And it is Naksu. Mu Deok was kidnapped and blinded in her childhood because she witnessed some event - perhaps the king's secret meeting with Naksu's mother? As a child, Naksu was sent to an astrological center and raised by a magician there who protected her and knew who she was, so he was able to read her horoscope, which included the king's star.
well, i think the real identity of Jang Uk together with the real identity of Mudeok and Naksu are the great mistery of the series. But so far about Uk we know :
- The King spent the night with Uk´s Mother in the body of Jang Kang. The series show us this.
- There is the prophecy of the star in the moment of Uk´s born. His father know this.
- We dont know exactly what his father believe because he didnt tell all for Park Jin, but he didnt want to kill Uk, but at sametime block his energy.
- Uk is very powerfull indeed. VERY powerfull. Can learn every magical stages very fast. He is a mage.
From this info, for me he is son of Jang Kang and the King at same time. He is a mage but is destined to be the King.