The Prince of Qin, Li ShiMin

At the end of the Sui dynasty, Emperor Li Guang begins to doubt the loyalty of General Li Yuan. In an effort to solidify the latter's loyalty, Li Guang decides to betroth his beautiful daughter Ruo Xi to Li Yuan's eldest son, Li Jian Cheng. However, Ruo Xi has already fallen mutually in love with Li Yuan's second son, Li Shi Min. This instigates a feud between the two brothers and their respective loyalists, eventually leading to the fall of the Sui dynasty and the beginning of the Tang dynasty.