Goong S (Korean: 궁S, Hanja: 宮S) is a spinoff of
Goong. It is produced by PD Hwang with the production company Group Eight. The main cast includes Se7en (aka Choi Dong Wook), Heo Yi Jae, Park Shin-hye, and Kang Doo. The series began its season on January 10, 2007, on MBC, and airs consecutive episodes on Wednesdays and Thursdays. This series is also known by the title "Prince Hours".
South Korea is a constitutional monarchy. The reigning queen (Myung Se Bin), already in her thirties, is not married yet and has no children, so the court looks for a Crown Prince. They encounter Lee Hoo (Se7en), a young man, the son of the empress' uncle. However, another competitor arrives at the court: Lee Joon (Kang Doo), the son of another uncle of the empress. They compete for the title of Crown Prince via a trial of several tasks to determine the worthy future king of the country.
Kang Hoo/Lee Hoo: A prince raised as a commoner because his mother was thrown out of the palace shortly before his birth. His mother died sometime during his teenage years and he was raised by one of the former Palace Guards, although Kang Hoo is unaware of the real identity of his guardian. The royal family was unaware of his existence until he was twenty and he was quickly taken into the succession line by his cousin, the Queen of Korea, because she was looking for a fitting successor for her throne. His name was changed to Prince Lee Hoo and he had to learn the ways and life of a royal. At the beginning, Lee Hoo seemed to be the least likely candidate to fill the spot of Crown Prince. He was rash, lacked focus and was seemingly selfish to most but as he struggled to learn of the life he was destined to live, he turned into a considerate, mature and responsible young man. He is also fair and has a great sense of right and wrong.
Yang Soon Ae: Prince Lee Hoo's childhood friend and one of the few that still refer him as Kang Hoo (the name he was raised as). She is a very sensible young woman who works at the palace as a palace maid. She has had crushes on Kang Hoo since they were young and has always been his friend. She seems insecure and jumpy but she has an exceptionally good heart. Prince Lee Hoo especially depends on her and she has been somewhat of his center. She kept cheering for Prince Lee Hoo for the best and later revealed her feelings and realized it is not a one-sided love. She also managed to attract the attention of Prince Lee Joon, the other candidate to fill the position of the Crown Prince of Korea, though she made it clear that her heart belongs to Prince Lee Hoo and only him.
Lee Joon: Raised by nobility, Prince Lee Joon seemed to be the best candidate to fill the position of the Crown Prince. He is exceptionally popular among the ladies and had his mind set to be the next King of Korea and seemed to be on the right path. He was shown as a calm and collective young man at first and was certain of what he wanted in life. He was to be engaged to the Prime Minister's daughter Shin Sae Ryung and agreed to the arrangement, but later resented it as he fell for palace maid Yang Soon Ae. He tried a lot of ways to persuade her into accepting his love but none were successful and he was rejected time after time. He later refused the throne after realizing that his father's greed was to no end and because he was tricked into believing that his father was not his biological father (in truth he is), he felt that he was not worthy to fill the position since he was not of royal blood. Later he learned the truth and was happy that he was able to pursue his own dreams of becoming a musician. He gave up on pursuing Yang Soon Ae as well seeing that she is truly in love with his cousin.
Source:
Wikipedia 
