Aku no Musume

A vast kingdom called Lucifenia, whose popular name was the "Kingdom of Yellow," was ruled by a tyrannical fourteen year-old princess named Riliane. Under her absolute monarchism, everything was exploited from people and the ones who did not obey her were executed without mercy. Allen, a servant who looked a lot like her, was always beside the princess whom Lucifenia's people called the "Daughter of Evil." The princess and the servant were the same age, since the two of them were actually twins who were separated shortly after their birth, with Riliane taking her mother's position as the country's ruler and Allen works in the palace as a servant since he was given up for adoption. The princess's selfishness and jealousy caused a war and many deaths, and their secret clockwork of fate was going to spin madly.

(Source: Vocaloid Wikia)