Crown Prince Sado
In 1762, his father, Crown Prince Sado, was executed by King Yeongjo (Crown Prince Sado's father and Prince Yi San's grandfather) after long conflicts and Sado's years of mental illness. Crown Prince Sado opposed the ruling party Noron party. Eight years later Yi San asked to visit Sado's living quarter but his Grandfather King Yeongjo refused. So he refused to attend Crown Prince Sado's funeral. On February 21, 1764, Yi San became the adoptive son of Crown Prince Hyojang and Princess Consort Hyosun by the order of King Yeongjo. Crown Prince Hyojang was the elder half-brother of his father, Crown Prince Sado. Crown Prince Hyojang though, had died during his childhood. King Yeongjo made Yi San a part of Hyojang's family because he was concerned that Yi San, who was Sado's son and successor, would be opposed. The Noron faction protested Yi San's legitimacy as the royal successor under the claim that Yi San was the 'Son of a prisoner' or 'Son of a psycho' and thus ineligible to succeed the throne. This was a major source of vexation for King Yeongjo for an extended period.