Following that, the old marquis went to the emperor to report back, repeating Gu Chengfeng's statement. He was probably worried that the emperor might become suspicious as to why their family's child would hide his talents, whether there was some secret scheme at play.
After the incident with the Quiet Empress Dowager, the old marquis clearly felt that the emperor no longer trusted him as much as before.
The emperor was still immersed in the immense joy of possibly being the birth son of the empress dowager and had no time to doubt this or that. He commended Gu Chengfeng and praised the old marquis for his exemplary instruction.
The matter with the Quiet Empress Dowager being the remnants of the previous dynasty did not require any further evidence. Her guilt was established, especially because she had stolen the late emperor's decree and plotted against the dowager empress of the nation. Her sins were grievous, unforgivable.