From an early age, he was proud and kept a filial attitude to his parents and siblings. When he was a child, he was praised for being sincere. His father,King Sejong was very fond of him.[3]
Like his second older brother,Grand Prince Suyang, he was proficient in martial arts, but he also created a scandal due to having sexual intercourse with court ladies and maids of the palace.
Yi Gu firstly married Princess Consort Nam,[4] but after a month of marriage, their marriage became problematic.[5] Despite the relationship, a son was born. But this led to the Grand Prince to marry Lady Choi of the Jeonju Choi clan, later being titled as Princess Consort Jean, as his second wife and later marry Princess Consort Ahn of the Andong Ahn clan as his third wife. Both marriages produced 5 daughters and 8 sons. He also had a concubine but no issue was born from the relationship.
In 1440, at the age of 20, the Grand Prince became theYeonguijeong.[6]
During the Gyeyujeong Rebellion, when Grand Prince Suyang fought for the throne against their nephew,King Danjong, Yi Gu supported and helped Grand Prince Suyang. Prince Imyeong greatly assisted Grand Prince Suyang and contributed to the enthronement of his brother asKing Sejo in 1453.[7]
