This special treatment would not be possible without special permission from the king himself.
This was explained by Lady Hyegyeong in her Memoirs.
There were different opinions on what happened between them, like Jeongjo making use of Hong Guk-young as a part of his plan to do a thorough clean up in order to break through the political influence and strengthen the royal authority, or Hong Guk-young grabbing the chance while leading Jeongjo astray for a short while.
Since he was Jeong Yak-jong's younger brother, Jeong Yak-yong was sent into exile for some months in Janggi fortress in what is now , having been found after interrogation with torture not to be a Catholic believer.
No, they were not all his concubines, but yes, they were forbidden from being involved in any other romantic relationships and had to dedicate their lives to serve in the palace.
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