The first son of Prince Yi Kang of Korea by Lady Jeong, he was a grandson of Emperor Gwangmu.

He was the eldest, illegitimate, son of Yi Kang, Prince Uihwa with Lady Jeong of Sugwandang Hall.

The remaining members of the royal family were also granted a new status, but not grand as their relatives and it was not officially included in the decree.

He was soon officially recognized as a member of the royal family only after the "Wang Gongga Gwebeom" (왕공가궤범; 王公家軌範) was promulgated in 1926.

Yi Geon entered the art department as a member of the 42nd class of the Japanese Military Academy.

On June 12, 1930, his father, Yi Kang, went into seclusion and inherited the throne, becoming the new owner of Sadong Palace and was now being called ‘His Highness, the Duke’ (공 전하).

On December 28, in connection with his admission to the University, Yi was transferred from being a horse riding instructor at the Military Academy to a member of the Guard Cavalry Regiment once again.

In a blood test, Momoyama discovered that he was not the biological father of his eldest son, Yi Chung, to which he believed that Yoshiko committed adultery back in 1932 when he was out working under the Japanese army.

Yi Geon suspected that her choice of employment would be trouble as Matsudaira worked at a Ginza club and was prone to be “too social” with the clients there.

Yi Geon and his family lived in a rented municipal house in Yono City, Saitama Prefecture.

Years later, his second son Momoyama Koya (桃山孝哉) served as vice principal of Kaisei Gakuin School.

An old military classmate and Japanese imperial family member Prince Mikasa came all the way to Urawa City to attend the funeral.

However, in the case of Yi Geon, he was naturalized as a Japanese citizen and was now of mixed blood with Japan, so there could be problems with legitimacy.