So, in this chapter, we see that the First Imperial Prince Un has very defined facial features. However, the Second Imperial Prince Bongrim does not. Now, with Intorno, everything has a meaning.
The Korean fans have commented that they believe the Second Imperial Prince Bongrim has been born with a deformity. That is also why they believe the Emperor does not consider him to be his child. I remember watching a Chinese Drama, and this is a trope that comes back often in Chinese contemporary works. The Emperor in that drama, namely Emperor Taizong of Tang, said: "The Crown Prince can be dead, but he cannot be a cripple." Though historically it is wrong to say that people with deformities were strongly rejected in ancient times (unless these deformities made them unable to accomplish their duties), it is a testament to how contemporary artists view deformities and believe these deformities were viewed in ancient times.
Another very interesting thing is that the Emperor talked about his doubts right in front of the woman who has given him two sons. The fact is, the Second Imperial Prince, by right of birth, since his mother is the Empress Consort, should become the next Crown Prince and eventually Emperor. However, China and Korea had heirs presumptive as opposed to heirs apparent. Which implies that they could displace a Crown Prince and give the title to another prince. What is the Emperor doing here? Testing to see how greedy Longhee is? Of course, any woman who would want her son to inherit the throne, and thus, raise herself to the enviable position of Empress Dowager eventually, would be well informed to feed the Emperor's doubts about the lineage of one of his other sons, especially if that other son is, by law, the next in line!!!
Emperor Sun seems to be playing, at this point, a sort of game of chess, testing his concubine as well as his chief advisor. No Emperor would ever willingly admit himself cuckolded!!! The humiliation attached to it could be worse than the humiliation of raising a son that was not his own.