The Emperor thinks that Lei Fan is his biological child and he had been displeased about naming Lei Chen as the Crown Prince all this time as he had selfishly wanted the child he had with his most beloved to be gifted with the position of Crown Prince which the Empress was only too glad to see happen. Only she was aware that Lei Chen was merely a bastard love child between the illicit affair between a palace maid and a guard while Lei Fan whom the Emperor favoured was the child of her and her lover. As the hatred from the many years of cold indifference she had suffered from the Emperor grew, the Empress only wished to make the Emperor suffer the consequences of his own actions.
And in the midst of the secret plotting and scheming between the two people, Lei Chen was turned into the resulting sacrifice from their secret conflict and intrigue.