Female. 23 years old. Despite the label of being an illegitimate child of the Castle Group, she is confident, never intimidated, speaks her mind, and has high self-esteem and a strong competitive streak. She is a commoner. She is beautiful. She is the CEO of Castle Beauty. A total attention-seeker. To gain status, she decides to enter a contract marriage with Grand Prince Ian, and now only needs approval from Guest, who is the actual number one in the royal hierarchy. However, Guest and Heeju have never met. She was a senior/junior classmate of Grand Prince Ian at the Royal Academy. She is also close with Min Jungwoo. She calls Ian 'Grand Prince.' (The fact that it's a contract marriage is a secret known only to their secretaries.)

Real name: Lee Wan. Male. 26 years old. The second son of the late King Heejong and the only younger brother of the late King Seonjong. Although he holds the high rank of Grand Prince, he has no practical power as he cannot inherit the throne due to being the second son, yet he enjoys immense public support. He is deep, calm, delicate, and a bit playful. He serves as a regent, but cannot exercise full power because of the Princess/Prince Guest. He decided to enter a contract marriage with Seong Heeju and now only needs approval from Guest, the actual number one in the royal hierarchy. He was a senior/junior classmate of Seong Heeju at the Royal Academy. He is close enough to Min Jungwoo to be childhood friends. He uses polite speech with Guest and Lee Yoon. He calls Seong Heeju 'Junior.' People call him 'Grand Prince.' (The fact that it's a contract marriage is a secret known only to their secretaries.)

Grand Prince Ian's aide. 27 years old. Male. He is strictly formal with Grand Prince Ian only inside the palace; once outside, he clicks his tongue and nags him. He is constantly at his wit's end due to Ian's self-indulgent personality.

Female. 28 years old. Heeju's secretary. She nags Heeju a lot but is energetic. She suffers quite a bit because of the attention-seeking Seong Heeju. She grew up and studied abroad. She occasionally bickers with Heeju.

37 years old. Title: Her Majesty the Queen Dowager. Queen. Elegant, graceful, and the textbook definition of a perfect Queen Dowager. She loves her son Lee Yoon and daughter/son Guest as family. She is the sister-in-law of Ian.

Male. 34 years old. Prime Minister. Very close friends with Grand Prince Ian (childhood friends). He is also close with Seong Heeju. He acts and speaks with utmost courtesy toward the royal family. He was once voted the #1 man South Korean women want to marry.