This is not a list of all the characters.  I will only specify the main characters in the story. 

Crown Prince:

Full Name: Wang Tae Yeon

Titles: Crown Prince Yeon, Wang Tae 

Crown Princess: 

Full Name: Jung Soo Yeon 

Titles: Lady Sooyeon, Crown Princess Sooyeon, Sooyeon 

Son of the Secret Royal Inspector: 

Full Name: Yi Hwang Joong (Inspired by Kim Jae Joong)

Titles: Lord Yi Hwang, Yi Hwang 

Crown Prince's Cousin: 

Full Name: Wang I Hyun (Inspired by Choi Minho)

Titles: Prince Hyun, I Hyun 

Lady Sooyeon's Servant: Sunkyu 

Crown Prince's Royal Palace Maid: 

Full Name: Hwang Mi Young

Titles: Court Lady Mi Young, Miyoung