Tang Taizong
By chance, Helan Xin'er arrives in a brothel. She meets the owner, who reveals herself to be the mother of the Emperor. The brother owner was once Empress Zhangsun's best friend and fell in love with Emperor Taizong of Tang. Empress Zhangsun betrayed her so the brothel owner switched their children at birth. Then who and where is Empress Zhangsun's child?