Like I said the prince takes full responsibility for the annulment. It is not hidden that (1) Neither of them like each-other. And (2) He likes someone else and wants to be engaged to them instead. He even actively goes to the King in order to try and get it to happen.

There was logic used that it was some sort of temporary love before they break up and he follows his actual engagement. This (1) absolves him of any sin of cheating since this was apparently expected to some degree. And (2) was f*cking s*upid given he pretty obviously wasn't just temporarily in love given he actively tried to make it official and this should of been known. And any logic that the fiancee shouldn't of known would then justify the prince not knowing the reason to his engagement via similar reasoning (The people they could talk to wouldn't of told them).

Next on to the illegitimacy of the second prince. We know for sure the second prince had a lacklustre education and most of his information came from his mother, the viscount by name. Including the fact he stayed in the palace most of the time can someone explain HOW THE f*ck WAS HE MEANT TO FIGURE OUT HIS ILLEGITIMACY, there is no mention of anyone actually telling him, the King almost definitely didn't give him anything to go off since

he ignores him and his mother and just leaves him (which makes this whole thing worse) and his fiancee's family didn't either (since the fiancee themselves knows he doesn't know and shows no concern) which is dumb.

Given no one who knows about the deal chooses to help him and his only source is highly biased it is SO s*upid to call the prince in the wrong here for the reason that he was "too dumb for not finding it out", wtf?

On that note the King is such a horrible person. The Prince's mother became a viscount in name thanks to her father's achievements and then became a consort to the King (why the f*ck someone who could make the King take in a consort didn't get an actual title..I don't know but let us ignore that). The king admits she didn't like her but she was pretty so f*cks her and the Prince was born... and due to the Viscount in name thing he was no claim to the throne and by rule he must go to his mother/in-law family when he reaches age. This is so f*cking irresponsible of the King on so many steps. Didn't give a proper title (seemingly had "none left"). Decided to show no support to the consort and let her be bullied (there is logic she is "dumb and only pretty" but if that is an actual reason to be bullied then this is wrong for a whole other reason). Decided to f*ck her and give her a son he knows she cannot take care of when he becomes an adult. Deciding to not at all take responsibility for that son to the minimum amount leading to the Marquis who was indebted having to make a deal. Deciding to not f*cking tell the son about it until it was already annulled and saying it was his fault.

Just all round wtf from me.

Will say their ending isn't even bad? He becomes a commoner with his wife, and they love each-other and have kids. While he cannot carry on the family business (doctor), their children can. And the major "loss" he had is that he isn't a Prince (which I don't even think he cared about) and that other might not like them (who cares?) and those that do must be cheaters or the like... which is dumb given they literally said it was normal in political marriage for them to have other relationships and is just.. wrong, even then it is also not that much a downside?

... after the engagement is annulled by the King.

He didn't publicly renounce his fiancé when he broke their engagement. He was very private about it, and even somewhat apologetic, despite knowing both of them never cared for the other. He fell in love, and instead of stepping on two boats, cancelled his scripted relationship to be with her.

Princes born of a concubine (which is NOT a setting in western fantasy, btw) are essentially sent off as son in laws, gaining the title and prestige of the bride's family while dropping their royal title. If they don't have a fiancé when they reach adulthood, they are booted out of the royal family with nothing, meaning they're treated even worse than princesses in the more extreme misogynistic (i.e. real world) settings. Ooookkkaaaayyy... so concubines exist in this s*upid world setting solely so a king can get his rocks off with someone who isn't actually his wife legally? They serve no purpose if their children can't even be reserve heirs. If the whole full-blooded royalty die, one of the duke's children will inherit the throne, the illegitimate princes have no chance at all. If this is the case, even a 'lowly' (sarcasm) viscount wouldn't want to send their daughter to be the king's concubine. Her children may grow up richly, but they'll just be married into another noble family if they're lucky, and it's a toss up on whether or not the daughter would get proper treatment at all. It doesn't benefit the noble or royal family. Only a commoner would benefit from the role (and the king who gets his rocks off cheating on his wife), yet the viscount's daughter had too lowly a position for it? What nonsense.

You're telling me he was never outright told about this rule? He was just sitting in his ivory tower, getting spoiled, and no one taught him his place? The king laughed at him (which I also find obnoxious) because he was unaware, but he had to rely on context clues that went over his head when he had no logical reason to suspect such a s*upid law existed in the first place! Rather than a 'serves you right' sort of feel, it feels more contrived than anything.

The King took no responsibility as a father and even laughed at his soon-to-be commoner son, enjoying via schadenfreude at his expense and the original fiancé never bothered saying anything or teaching him his role as the marquis' husband (she was cheated on by him, technically, so that's not big, but did they know each other at all?)

Children born of concubines are not considered fully royal. Upon reaching adulthood, they are married off into noble families (I think it was stated that they had to be at least of the same rank as their maternal family line but the translation was a little weird) without gaining the title. Basically, a former prince would marry in as a son-in-law but would only be the spouse of the woman who inherited the title (kudos on being progressive here).

The concubine has been telling the Prince that she doesn't go out to interact with the King's other wives (kudos on not being progressive here) because they don't like her and torment her. Turns out it's because she had her father practically force her way into being a concubine through the life debt owed by the MC's grandfather. The concubine understood nothing of the nobles and had such a terrible personality that the MC's family refused to allow her to be adopted in.

The concubine also never explained to her son that he would not inherit a royal title as he was not the son of the Queen. Which is why he willingly broke off his marriage with the MC despite everyone telling him to work hard to help her.

I'm sure many people already told him the reality since a long time ago that he couldn't inherit the throne and couldn't even stay at the palace after he married because his mother didn't have a high status (it didn't make sense though). So, in other word, he could only be a son-in-law in other household. That's why marrying FL was the best choice because he could be a marques in the future.

But since the author made the prince so dumb, I guess he couldn't understand his predicament even after being told about that fact.

Julius as a second prince is an idiot by his mother upbringing and fake story that they are loved by King. That is why he misunderstood that he will recieve the throne after his father and he can make his lover his Queen, he didnt listen to other that include his father that he will have to support Alicia who will be the head of her family in the future but retorted it to she is the one who support him instead.

He likes a pure maiden that believe world is move by pure love though he didnt know that his mother is not loved by his father. (I kinda think the King is happy that Julius is ruined his own life and bring his mother down togeter he must saw her as an eyes sore.). He dont have sense of duty and manner, and dont think anything about the device given by other much, if he like that idea he will do it if not he ignore it. Yeah, that how idoit he is.

Ps. I want to know how is his life after become a commoner But it wont tell much in the end.