SPOILER!!
so the thing is claude's brother (Anastacius, the previous king), is actually dead- the only reason why he slept with penelope (jennette's biological mother and claude's ex fiancee) was to make a child born from black magic. Anastacius knew somewhat the claude was planning on killing him, so he planted black magic inside Jennette when she was just a fetus. The black magic made Anastacius's soul still exist, but he could get revived when Jennette absorbs Claude's life force and mana (I think). In the original book, 'The Lovely Princess,' where Anastasia was falsely executed, Claude dies after Jennette unintentionally absorbs all his mana and life. Then, Anastacius comes back to reclaim the throne since he is revived because he got enough of Claude's life force. There are two endings in the og book.
1st ending: Jennette dies by Claude's side and Anastacius rules the Obelia empire by himself. But I think Jennette uses the last portion of her black magic to wish for everything to start over again, except the Princess gets all the love from Claude and Claude disliking her (that was the price to give the princess happiness). She truly loved the Princess, and felt super sad when she was falsely accused of poisoning Jennette. The real culprit that poisoned Jennette was her aunt, who wanted to falsely accuse Anastasia so that Jennette was the only line to the throne. So Claude and Jennette die together and time rewinds. However, Jennette didn't keep her memories. Only "Athy" did, as a reader of the book. (MEDIOCRE ENDING?)
2nd ending: Anastacius offers Jennette to stay by his side since he is her real father, and she agrees. Jennette goes marbles and loses rationality. She thinks stuff like 'Yeah...a father that kills his own brother to be king is worse than a father using his daughter to live...I should just stay as heir' something along those lines. (BAD ENDING)
well it's been a while since I read the novel but it was something like this ^^
FLUFFY SPOILER AWAY FROM THE ANGST!
before the end of the manhwa lucas and athanasia should probably kiss a couple times, considering the novel's events :P
ONE MORE SPOILER!
on athy's 15th birthday, lucas plans a big surprise to give to Athy for her birthday. The big surprise was Claude regaining his memories.

Why do I ship jennet and that guy I don't know and