
Ethel is the only legitimate prince to the Emperor when this is revealed all those who looked down on him will eat their words trying to appease him.
Rezef is not the Emperor's son he is the result of the late Empress affair with Raphaello's dad who is an utter shitbag and waste of space.
The Emperor found out the Empress cuckolded him with the lowlife and killed her using her allergy to almonds. He made up a story that Rezef was his bastard to:
1. Cover up the fact the Empress cuckolded him
2. Punish the late Empress that her son will labelled a bastaed
3. It would mean Rezef is not automatically entitled to be his heir - he doesn't want Rezef to be his successor.
Cayenna turns on Rezef after he does something unforgivable - murders her Nanny and frames it as a suicide. Suicide is the most disgraceful way to die within their society.
He does purely out of Jelously because Cayenna loved her Nanny very much. More so than her mother.
After this there was no point of return and she realised Rezef was beyond rehabilitating.
So she decides to take away the thing he wants the most - the throne.
Rezef is manipulated by the Empeor into killing his biological father who is eager to meet
him (the father considers Rezef his "real son" and hates Raphaello despite being a parasite living off the Kedrey status and money of the family he hates so much)
When rezef realises the Emperor set him up he goes beserk and ends up killing the Empeor.
Cayenna becomes Princess Regent assumes the role as a temporary Empress until Ethel is 20 and considered old enough to rule.
Ethel marries Olivia and she becomes his Empress. They have a daughter.

A lowlife misogynistic parasite.
Gets himself into debt and fails running a business...
Decides to sell his daughter for money to cover the financial hole HE caused.
If that wasn't enough he steals the money that was suppose to be HER marital allowance for his own selfish uses.
Taking away her opportunities to study or become independent. Neglecting to hire a carer for her grandmother and instead making her do the work while he leeches her money for his failed business ventures.
Her father was a scumbag. But a typical one by Japanese comics standards.
You can't offer to be someone's escort and then jilt them seconds later in front of them, when someone else shod up.
I heard this is an original webtoon so we have no spoilers yet.