Hwa Yun, also known as Lady Hwa, was Cheon Yeo Woon's Mother and the beloved wife of Cheon Yu-Jong. She was poisoned and died when Yeo Woon was little.
SPOILERS
Later on, it was revealed by Cheon Jongsum that the one who poisoned her was Lady Mu of Dark Clan . Sister of Mu Jinwon head of the Dark clan . She was also the wife of Cheon Yu-Jong 23rd Demonic Lord of The Heavenly Demonic cult.