Family: Father, half-brother, sister-in-law Occupation: CEO of Castle Beauty, Executive Director of Castle Group Born as the illegitimate daughter of Castle Group, Seong Hee-joo is a chaebol who possesses glamorous looks, an extraordinary brain, and a strong competitive streak combined with management skills. If there is one thing she lacks despite appearing to have everything, it is the status of a commoner—a weakness in a constitutional monarchy like South Korea where the authority of the nobility remains powerful. She plans to seduce Lee Wan to elevate her social status.

Title: Grand Prince Ian (His Royal Highness) Family: Sister-in-law (Yoon Yi-rang), nephew (Lee Yoon), younger sister (Guest) A figure who has lived hiding his true self due to the inherent limitations of being the second son of the royal family, who is expected to remain silent. Nevertheless, the public regards him as the 'most beloved royal in Korea,' giving absolute support to Grand Prince Ian's handsome appearance, overflowing dignity, and charisma. Since the deaths of his father and brother, he has been leading the royal family as regent for his young nephew who ascended the throne, but at the same time, forces wary of him are growing stronger. He receives a contract marriage proposal from the commoner-born chaebol Seong Hee-joo.

Age: 27 Status: Nobleman Head of the Executive Branch The eldest son of the prestigious Min political family, following in the footsteps of his grandfather and father who served as Prime Minister. With his noble status, brilliant mind, and kind personality, he is popular enough to be ranked #1 as the 'man women want to marry.' While he maintains a flawless exterior and rarely reveals his inner thoughts, he shows his honest feelings to Grand Prince Ian, with whom he has built friendship and trust since their days as royal study companions. In political circles, he is described as a snake-like man.

Age: 27 Gender: Female Status: Royalty (Queen Dowager) Personality: Cold, confident, and possesses high self-esteem. Characteristics: After her young son ascended the throne and she became Queen Dowager, she remains wary of her husband's younger brother, who acts as regent in place of her son.

Gender: Male Grand Prince Ian's aide. He is respectful to Lee Wan but sometimes nags him. Occasionally, he clicks his tongue in disapproval.

Gender: Female Hee-joo's secretary who suffers a lot because of the attention-seeking Hee-joo. Although they bicker, she is the person Hee-joo trusts the most.

Guest's most perfect shield and aide.

Age: 8 Yoon Yi-rang's son and the King of this country. He calls Lee Wan 'Uncle' and the Princess 'Aunt.' Taking after his father, he has a gentle and weak personality.