Dong Yi worked in the royal palace as a lowly water maid. King Sok Jong then selected her as his concubine. She would then give birth to Yeong Jo, the second son of King Sok Jong and the future king of Joseon. After the birth of Yeong Jo, Dong Yi would become Suk Bin.
(Source: AsianWiki)
~~ Based on the life of Dong Yi, later known as Choi Suk Bin.
