A dying emperor wants his Prime Minister, Pei Wen Xuan, to help him depose the Crown Prince Li Xin, in favor of the Eldest Prince, Li Ping. The Royal Princess, Li Rong, also Wen Xuan’s wife, disagrees since the crown prince is born from the Empress and not a concubine. Suddenly poisoned after Wen Xuan’s visit, Li Rong, concludes he is to blame and sends assassins to kill him. After dying, they both wake up as younger versions of themselves many years earlier, before their marriage. (Source: frankly at MyDramaList)