"This was the Crown Prince's plan, the one the Emperor had once devised. If it weren't for the appearance of Master Yin He, the current situation..." Ju Nanyi immediately spoke up, despite not knowing Zheng Congyuan's plan. However, with Ju Nanyi's intelligence, from what Prime Minister Lin knew, and from the actions of Qiandao Temple, he quickly figured it out.
Moreover, in Chenyuan Hall, Zheng Congyuan abandoned everything else resolutely, just to have Zheng Nianru, which confirmed his suspicions.
One could say that all of this was brought about by Zheng Congyuan's own doing. He could have controlled the Wen Family quietly, but instead, he deliberately led them to start a rebellion. He even exploited the prophecy of Qiandao Temple and the talk of the Child of Heavenly Selection, to place the entire Nanzheng in jeopardy. Zheng Congyuan even risked himself, all to make Zheng Nianru's ascent to that position seem just and natural.