The prince was born on 20 October 1897 at Deoksu Palace in Seoul as the seventh son of Gojong, the Gwangmu Emperor.
His mother was the Honorable Princess Consort Eom Seon-yeong, a palace attendant, who was posthumously awarded the title of Princess Sunheon.
He was also the younger half-brother of Emperor Sunjong and Prince Imperial Ui.
He was titled Prince Imperial Yeong in 1900, and became the crown prince in 1907, despite being younger than Prince Ui.
Prince Ui's support base at court was not strong because his own mother, Lady Jang, had already died.

In December 1907, he was taken to Japan on the initiative of Itō Hirobumi to be enrolled at Gakushūin Peers' School.
The move was meant to ensure that the Korean royal family would not take any further anti-Japanese actions following The Hague Secret Emissary Affair.
Japanese Emperor Meiji, who largely ignored his own grandchildren, devoted a lot of attention to Yi Un, acting as his guardian.
Itō would bring Yi Un whenever he was visiting the princes Hirohito, Chichibu and Takamatsu.
Meiji apparently stopped seeing Yi Un so frequently after Ito's assassination.
 Yi Un was allowed to visit Korea again only after the death of his mother in 1911.
The prince was born on 20 October 1897 at Deoksu Palace in Seoul as the seventh son of Gojong, the Gwangmu Emperor. His mother was the Honorable Princess Consort Eom Seon-yeong, a palace attendant, who was posthumously awarded the title of Princess Sunheon. He was also the younger half-brother of Emperor Sunjong and Prince Imperial Ui. He was titled Prince Imperial Yeong in 1900, and became the crown prince in 1907, despite being younger than Prince Ui. Prince Ui's support base at court was not strong because his own mother, Lady Jang, had already died.
In December 1907, he was taken to Japan on the initiative of Itō Hirobumi to be enrolled at Gakushūin Peers' School. The move was meant to ensure that the Korean royal family would not take any further anti-Japanese actions following The Hague Secret Emissary Affair. Japanese Emperor Meiji, who largely ignored his own grandchildren, devoted a lot of attention to Yi Un, acting as his guardian. Itō would bring Yi Un whenever he was visiting the princes Hirohito, Chichibu and Takamatsu. Meiji apparently stopped seeing Yi Un so frequently after Ito's assassination.  Yi Un was allowed to visit Korea again only after the death of his mother in 1911.
Yi Un