In which episode of Princess New Zhu Huan did the emperor know that Wei Zi was a real princess?

In the 49th episode, the Queen reported to the Queen Mother that the emperor wanted Wei Zi to become a nobleman. The queen mother was so frightened that she only said that she would handle it herself, but the queen took the opportunity to suggest Yongqi or Swallow to marry Mongolia. The Queen Mother considered the overall situation from many aspects. In order to protect the emperor's face, she advocated that the swallow should marry Wei Zi to Mongolia. Unexpectedly, Seya chose Erkang as her mother-in-law. The situation was urgent, and everyone finally told the emperor the "truth" that the queen mother could not control. Egged on by the queen, Swallow, Wei Zi and Jinsuo were put into Zongren Palace for investigation.