Aconite

I was born to take my father’s throne from you, Anna –

Aconite is played by Alexandra Serova. She is a secondary antagonist in the later seasons of Mabel.

Season Six
Aconite appears first in Primogeniture. She believes herself wholeheartedly to be the daughter of the King and challenges Anna's right to the throne.

For her full backstory-- WITH WARNING FOR SPOILERS UP TO EPISODE FORTY-- you can check this page.