About Yi Un
Yi Un (이은; 李垠; 20 October 1897 – 1 May 1970) was the last crown prince of the Korean Empire, the head of the former Korean imperial house after 1926, and a lieutenant general in the Imperial Japanese Army. He was the seventh son of Gojong of Korea and the son of Imperial Noble Consort Sunheon. Yi Un was designated crown prince in 1907 and was taken to Japan later that year for education under Japanese supervision. After the annexation of Korea by Japan in 1910, the former Korean imperial house was incorporated into the Japanese-created ōkōzoku system. He married Princess Masako of Nashimoto in 1920 and succeeded Sunjong of Korea in 1926 as Yi Wang (李王), the Japanese-recognized head of the former Korean royal house. Yi Un served in the Japanese army, reached the rank of lieutenant general, served on the North China front, commanded the First Air Army, and was appointed a military councillor near the end of the Pacific War. After Japan's defeat in 1945, he lost his royal status in Japan and remained there until South Korea permitted his return in 1963. He returned while seriously ill and died at Changdeokgung in 1970. His mother was the Honorable Princess Consort Eom Seon-yeong, a palace attendant, who was posthumously awarded the title of Princess Sunheon. He was then enrolled in the 29th class of the Imperial Japanese Army Academy, from which he graduated on 25 May 1917 with an excellent record. Before becoming the heir apparent to Sunjong of Korea, who became the emperor in 1907, Yi Un was known as the title Prince Imperial Yeong (영친왕). On 10 June 1926, upon the death of Emperor Sunjong, Yi Un received the late emperor's title, and became the King Yi of Changdeokgung (昌徳宮李王), which referred to the palace Changdeokgung.
Biography source: Wikipedia. The profile adds birthday-specific historical context from the Celebs Birthday Today editorial database.