After Tang Yanqi left, he inadvertently learned about her identity from his mother. His mother told him that before Tang Yanqi left, she mentioned this when handing over the divorce agreement.
She said she wasn't the noble daughter of the Tang Family. She was just an illegitimate child, and perhaps because of this, she felt guilty towards him, and therefore gave up the shares of the corporation given to her by Mr. Sheng.
He learned more about the details from Tang Ruhai. Originally, the young daughter of the Tang Family, Tang Wan, was kidnapped in her childhood and met with an accident. That was why the Tang Family brought back the illegitimate daughter they had left outside.
Sheng Jianan remembered that he had asked about Tang Yanqi's mother because if she left, it was highly likely she was going to find her mother. But Tang Ruhai told him that Tang Yanqi's mother had passed away.
