Nulliitas: The Half-Blood Royalty is a Manga/Manhwa/Manhua in english language, Drama series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.nl fastest updating comic site. The Summary is

Dreaming to be a knight, an unnamed girl who grew up as a boy. In fact, she was actually the illegitimate child of Count Romagnolo, who she worked under as a servant. Eventually, the Count found out her existence, and she was sent as a replacement bride for her blood-related sister that the Count endeared more. So she was given the name “Núllǐtas”, and let’s see how her life changes onward.