How did Jiang Xinghuo know that his father Zhu Di had promised him a big cake of "how sick the son is"?

The reason why Zhu Di dared to turn his back on this matter was that apart from the two of him, there were only a few guards around him who heard about it, and there were no witnesses of any weight.

It was precisely because of this that no more than ten people in the entire Ming Dynasty knew about this matter.