Izyda:
I'm not sure there was a love scene. I think Jang Kang somehow stopped the king, and he doesn't know it himself. Or it was just his imagination that made him believe it. Probably Do Hwa was already pregnant and the King found out about it through Jin Mu. All this was to serve only as a basis, because for me, the king did not want to have a descendant, but only he wanted to receive another life and reign again. 

The king himself said he wanted a son because of the divination he received when he ascended the throne.  

 Izyda:
Yes, the star of the king appeared in the sky when Jang Uk was born, but as for me it happened not because he is the son of the king, but because he will deserves it and the assembly of magicians will choose him as the new leader.

There's literally no reason to doubt what happened during Uk's conception. Unless the writers showed nothing but lies to us, which does not make sense, we have to believe the scenes we have until now.
1 - Kang was too weak to stop the king to have his wife.
2- There was no time for Jin Mu to learn the alchemy of souls in time to stop the king.
3- The king thanked Jang Kang after switching back their bodies.
4- Jang Kang's actions point to the fact the Uk is indeed the offspring of the soul shifter king.

 Kathryn_51:

That's the best idea I've heard from anyone.  Jang Uk earns it  - doesn't inherit it.  Very good!?

( I couldn´t quote the other answer)

 But  what is exactly the prophecy? The star of the king will appear for the King´s son or for the next King regardless of the  blood relationship?

 Cau:

( I couldn´t quote the other answer)

 But  what is exactly the prophecy? The star of the king will appear for the King´s son or for the next King regardless of the  blood relationship?

The divination was: the king would be granted a son who had the energy of the King's star.

About the King's star:
"The star at the center of the Big Dipper that contains nature's secrets only reveals itself when the sky is filled with the energy of the Daeho waters."

 jxxwxxstan:

The divination was: the king would be granted a son who had the energy of the King's star.

Thank you. It was what i remembered. 

So I maintain what i think, Uk is the son of both Jang Kang and the King. Unless the writers modified things in the future. haha

I really wish his mother was already pregnant but it seems its not the way things were.  

 Cau:

Thank you. It was what i remembered. 

So I maintain what i think, Uk is the son of both Jang Kang and the King. Unless the writers modified things in the future. haha

I really wish his mother was already pregnant but it seems its not the way things were.  

Yeah. Even if Uk is 100% genetically Jang Kang's son, the king was the one who planned his conception and was consciously there with Dohwa.

This may also be true, especially since I thought Jin Mu had planned everything in advance with the previous king. But it seems that for the first time he had contact with the king when the king called him to himself, it was then Jang Kang was in his body and asked him for help.

Definitely, the Naksu's family was not killed because of Jang Uk's horoscope, because in episode 5, Jang Kang revealed to Park Jin that he had already left fake plate (somehow I missed that). So no one knew the truth. Of course, apart from them and the person who made it (could it be Naksu's father? We don't know that yet). So probably Naksu's father died because there was another soul shifter in his body. In order to seize power in Cheonbungwan, Jin Mu, who was exiled from the Jin family and taken in by Jang Uk's father, wanted power and decided to bring misfortune to Cheonbungwan. And learning alchemy of souls allowed him to do so. I believe he himself was possessed by some evil spirit from Jinyowon.

What if the previous king simply couldn't have children because he was sterile? And is the king's star related to birth? Probably not. If it is owned by an individual outside the royal family, it could mean a treason seizing power.

 Conservative_Torch:

I suddenly thought of this while rewatching the 1st episode.

Naksu only had 1 blue mark on her shoulder after she soul shifted.

But Mu Deok technically have 2 blue marks (eyes) on her body. 

Does that mean Mu Deok her self might be another soul shifter?

This can be true. Maybe Naksu and the elder sister of the Jin family are both in Mu Deok's body. We do not know what age a representative of the Jin family would have been when she was kidnapped or missing, but to survive in a body other than her own, she would have to achieve the appropriate level of magic. Her sister is sad about her death. Since she believes she is dead, do Jin's family have her body? On the other hand, if I remember correctly, is her father looking for the missing sister? If there was a body, it would make it possible for the soul to return to the body, because the mages in Daeho can keep the body from decaying, but for how long?

 Conservative_Torch:

That was Jin Cho Yeon dear

Clearly I'm totally incapable of understanding anything about this drama :P

Nevertheless I'm enjoying the show.

 Thecla:

Clearly I'm totally incapable of understanding anything about this drama :P

Nevertheless I'm enjoying the show.

It wasnt your fault, it was not that clear, the mirror thing btw.
 
On that note..since @Conservative_Torch mentioned and I agree its Barbie mage, sorry I meant Jin Cho Yeon, could the mirror be a reflection of the opposite of your desires? Your deepest darkest evil?

So what we see next week is basically Mu Deok's (or is that Naksu's?) innermost desire, that's why we see her kissing Seo Yul and Crown Prince, something Naksu would not do IRL. That mirror has got nothing to do with her being eldest Jin daughter. 

 Izyda:

What if the previous king simply couldn't have children because he was sterile? And is the king's star related to birth? Probably not. If it is owned by an individual outside the royal family, it could mean a treason seizing power.

We already ascertain he was too weak to have children and know he has been trying which is why he was desperate enough to try soul switching and using daddy Jang's body to impregnate mommy Jang (see ep 1 when old king was first introduced, it was one of his first lines to Jang).

The look of shock from daddy Jang about the request was because he knows soul switching was illegal and he didn't think King would be using his body to impregnate his wife.

Now the interesting thing about this is, why did the King go for mommy Jang? I'm sure he has hundreds of concubine in the palace but he chose to be Jang. We know mommy Jang is a looker coz uncle Park (current head of Songrim is still single) but could it also be because mommy Jang is magically powerful too?

 Kim Hee Soo:
Now the interesting thing about this is, why did the King go for mommy Jang? I'm sure he has hundreds of concubine in the palace but he chose to be Jang. We know mommy Jang is a looker coz uncle Park (current head of Songrim is still single) but could it also be because mommy Jang is magically powerful too?

He was inside Jang Kang's body and Dohwa was his wife. I mean, why go to a concubine if you can be with the woman who used to be considered the most beautiful in Daeho? That would also not taint Kang's image, he was doing the king a favor after all.

ah yes the most beautiful in Daeho..i forgot that bit hehhe and yes the King isn't such a scumbag after all, he still respects Jang Kang.

 Kim Hee Soo:

ah yes the most beautiful in Daeho..i forgot that bit hehhe and yes the King isn't such a scumbag after all, he still respects Jang Kang.

In Jang Kang's body, he could not spend the night with the king's concubine, it was forbidden. All the women in the palace belonged to the king, especially his concubines. If I were the king, I would also choose Jang Kang's body because he was a powerful mage and his offspring might even surpass him. And only Jang Kang knew the alchemy of souls. Of couse his wife could be a mage too.