Crown Prince Hyojang (Korean: 효장세자; Hanja: 孝章世子; April 4, 1719 – December 16, 1728), personal name Yi Haeng (이행; 李緈), was the first son of King Yeongjo of Joseon and his concubine, Royal Noble Consort Jeong of the Hamyang Yi clan.
[1] He was born during the reign of his grandfather King Sukjong, but his birth was not made public, because his biological grandmother, Royal Noble Consort Suk, had died the previous year.
In 1762, Sado was imprisoned in a wooden rice chest at the order of his father, King Yeongjo, and died 8 days later, leaving his son, Yi San, as the only royal male heir.
Yeongjo was concerned that Yi San, being Sado's child, would be branded as "the son of a sinner" and thus become ineligible to succeed the throne, so in February 1764, he decreed that Yi San would become the adoptive son of the long-dead Crown Prince Hyojang.
[4] In spite of this, Jeongjo respected the wishes of his grandfather and honored his adoptive father as King, and granted him the temple name Jinjong (진종; 眞宗).