The Last Princess depicts the tragic life of the last princess of the Joseon Dynasty, Princess Deok-hye, based on Kwon Bi-young's novel Princess Deokhye. Although it is a historical drama rooted in actual events and figures, it incorporates significant fictional elements, making it a 'factional' historical film. Born as the beloved only daughter of Emperor Gojong, Princess Deok-hye was forced into exile in Japan after the fall of Joseon. There, she reunites with her former betrothed, Kim Jang-han (Park Hae-il), and plans an escape to Shanghai with her brother, Prince Imperial Yeong. However, the plan fails, and Princess Deok-hye is forced into an unwanted marriage, unable to return to the homeland that she had longed for all her life. Forgotten by people, she is eventually discovered in a Japanese mental hospital by Kim Jang-han in the 1960s.