His father was the son of Crown Prince Sado and his great-grandfather was Yeongjo of Joseon.
During his early childhood, he was adopted by Hong Guk-yeong, the fourth cousin-once-removed of Lady Hyegyŏng, as the son of his sister, Royal Noble Consort Won of the Pungsan Hong clan, and King Jeongjo.
At the time, Ku Seon-bok and other Joseon noblemen supported Yi Jun as heir to the throne, but as King Jeongjo was in his mid-20s and could still be expected to produce a child, Kim Jong-su, along with many of Jeongjo's ministers, who were enemies of Hong Guk-yeong, demanded his and Crown Prince Wanpung's removal.
[1] On November 20, 1786, Prince Sanggye suddenly died and it's suspected to have been poisoned.
After his death, he was buried at Yeonhul Castle, near modern Sinchon Station and Yonsei University.