Please recommend a novel about transmigrating to become an empress.

I only read the beginning: The female protagonist had transmigrated to become an empress and had a son (who seemed to be the crown prince). She was not favored. There was a very long description of the Empress's identity in the text: The Empress's father had once saved the late Emperor. The late Emperor had originally promised his father that he would make her his son's wife, but in reality, the late Emperor was not willing at all. Later on, her father and she disappeared. A general found the empress and brought her back. Before the late emperor died, he was in despair, but everyone thought that he was extremely sad because he had found a benefactor. I forgot the title of the book. Thank you for telling me.