@lissikukk Ah no. That's not what happened in the first life. First, she was adopted, taught the mannerism of the high society so that no one would suspect her. Then her family, the grand duke killed Cecilia, the girl you're talking about as the crown prince's gf or whatever, who was the empress then, meaning his wife. Since I assume the crown prince is not an idiot who doesn't remember the details shown, it can be presumed he knew about the Grand Duke's crime since the next in line of power was Elena (or Veronica who she was impersonating), as the queen. It makes sense why he hated her.
Hope you understand it's not "So ml has a girlfriend but still marries mc and treats her like a trash".