
Spoiler
At this scene. The duke was shocked the Damian was calling Lucia as "Lucia". The duke don't know that name. He said "He don't call her mother or vivian. He calls her Lucia. A name I don't know". The duke didn't ask Lucia about this, but he keeps questioning himself why damian calls her different. Why doesn't know that time. Then he investigate and found out that it's her childhood name. He said "Why she didn't tell me about her childhood name".
Plus, the duke often get envy of Damian. How he's so close to Lucia. Even after Daian left the mansion. Lucia and Damian always writes each other. Plus Lucia often send damian a embroidered handkerchief. Then one time, The duke stole the handkerchief that is supposed to be Damian's handkerchief then since that time, he's always carrying a handkerchief.
On the day Damian will leave the mansion. He finally calls her "Mother". Since then he addresses Lucia as mother and Duke as father. Damian was officially registered as a family.

Hmm. Was Helion being threatened? Maybe the reason why he's being like that because he's being threatened.
Anyway, I know Helion truly loves Agatha but in a toxic and possessive way. Just sad. I wish he won't get a concubine. If he did. Gonna drop this manhwa, not worth for headaches lol.
Anyway, maybe the reason why Helion is keeping agatha from throne/duties is either because he don't want her to be entangled in politics/be in danger. Or Helion feels threatened of Agatha's right to the throne, since she's the direct descendant of the previous king, like Helion wanted the throne by himself
I SWEAR THEIR SEXUAL TENSION IS TOO MUCH FOR ME (⊙…⊙ ) Damn. They're PERFECT MATCH FOR EACH OTHER. THEY LOOKS SO GOOD TOGETHER Everytime they both talk, flirt, kiss, then in the bed. Ugh., i can't handle the sweetness and sexual tension hahahaha. It's so cute when the king blushes hahaha. He's too head over heals in love with her