Oh. Thank you, I remember now, Sybilla is the queen who was killed by the king.
This was revealed to be a lie. Alaina, the elven teacher, is believed to have killed Sybilla after Sybilla killed the King.
So the current king is actually the eldest son of the Red Emperor? At the beginning, didn't the male protagonist's male magic teacher say he was in the dungeon? Was he released by the female magic teacher to become king?
Yes. Alaina basically set everything up with the help of her allies and the eldest son faction, if I'm not mistaken. Because the Eldest son looks like his younger brother, it was somewhat easy to fool everyone. The ones they couldn't fool, they killed to cover their tracks.
So to recap
Alaina is the elven teacher of Elis at the start. She's some kind of noble elven lady like Elis mother, the current Queen. Them possibly even being cousins. She basically manipulated the entire kingdom to get the king to marry an Elf.
Sybilla is the former Queen. She killed the King and with Alaina help, she covered it up. Later on, she is supposedly killed by Alaina since she obviously knows the truth.
Cass is the daughter of Sybilla and the second son of the emperor. Priscilla is her aunt.
The current King is Elis, Elin and Lia father. I won't include my theory of him also being the father of Elis cousins Arion and Noira because it's not confirmed yet and I don't want you to get confuse by something that might not be true. Even though I think it is true.