He already heard what happened, when he came to the imperial hospital.
He had thought that Lady Chaoyan's major achievements were that she was accepted by Saint College. He assumed that she felt a bit interested in medicine. However, he had not expected that Lady Chaoyan would be so skilled at medicine, and that she managed to save the Young Duke who even the imperial doctors failed to save. As a result, Chaoyan saved the Young Duke who was now in a steady state.
In this way, not only did Duke North's Mansion owe Lady Chaoyan a favor, but she was also going to be very popular as a doctor in the capital. Therefore he was even more determined to marry her.
Even if Lady Chaoyan might not be the Phoenix Girl, her being next to him would still boost him up. He was willing to promise her a lifetime of luxury.
With these thoughts in his mind, Lord Ling found Gu Chaoyan increasingly interesting and beautiful.