Uragirareta Akutoku Oujo, Youjo ni Natte Reiketsu Koutei ni Hirowareru

Princess Euphemia, boasting the most magical powers, talent, and beauty in her country, is known as the evil princess due to her arrogant attitude. One day, she's betrayed and nearly killed by her fiancé and sister. She barely escapes with her life, but...the next thing she knows, she's been transported to a distant land and transformed into a little girl! Then, she's picked up and protected by Albert, the emperor of another country rumored to be the "cold-blooded emperor"...

(Source: Jitsugyou no Nihonsha, translated)