It’s pretty obvious it’s because his family was exterminated just because of meeting him, and this would be the reason the least prominent. The other reasons would be that after executing and declaring their clan a treacherous one, his older brother was made into a slave, and after that he was brought as “crown princess” to the palace to marry the man whose father ordered the extermination of his kin; and to top it all off, his older brother died and was brought back to life in a dangerous way solely because he was the crown princess… I would be even more pissed off if I were his sibling, tbh (let’s also not forget, Hyo lied about his identity —which made sense ofc—, only to have little Doram looking for whom he thought he was and getting arrested and traded as a slave)
Yes, I know those plausible reasons. The very reasons Doram have had his emotions tangled. What I implied is that, Do-un experiences and understanding of those deeds aren't (or sort of shouldn't be) nearly apparent as Doram, coz he was not involved or aware of all those hopes and disappointments. Hence, I understand he would not "like much" the prince and actually understand better logically than Doram. So for him to be this hostile...is making me worried

Though I understand Doram's emotions, for all the valid reasons, I wonder why Do-un dislike him as well