Nope, MC and ML didn't knew that the other one was reincarnated. The only one who knew ML was reincarnated was the other prince, (I forgot which one). This other prince was also a reincarnator. The other prince also born from some nameless concubine, he used to be scum male who had many concubine, his previous end is almost the same as ML, with the difference, his Princess Consort actually stood by him. He realised how scummy he had been and after he reincarnated he turned new leaf and to avoid suspicious, he pretended to be indulgent by eating alot (he became fat). He didn't want to battle for the throne because he thought it was too bothersome so he approached ML because he concluded from ML’s different action that ML was also reincarnated. His relationship with his princess consort was actually hilarious because the princess consort is a tsundere. On the other note, I personally didn't think ML's princess consort was very evil, so I actually feel kinda sorry for her in the end: 1. She young and was forced to marry ML and separated from her lover by her family. So at the beginning she rejected ML and said hurtful things toward him. 2. ML was as we know not very socially educated and was not able to manage his inner yard, past ML thought that it was all calm and fine. ML had many concubine, she had to fend all of them, and one of her child also died because of one of the side-concubine. 3. Due to the death of her child, she thought that ML was unreliable, so she had to relied on herself to protect her and her child.