hide and cultivate in the east palace, only to find the prince is a girl

It was 12 years ago.
The empress gave birth to a princess. She declared to the public that she was a boy, named Xia Shimin.
Three years ago, Xia Shimin was made the crown prince and arranged a marriage with the present Grand Preceptor's daughter, thus securing the imperial power.
......
Zhang Ronghua crossed over at her birth. As a proper forbidden soldier, he has been hiding out for 15 years in the royal residence. Every day that passed, his talent would increase by one point.
Seeing that the wedding date was getting closer, he accidentally found out that the crown prince was a woman.
The night of the wedding.
Prince: I need you to marry me!