I don't know why Regina had to act like that to Ellen. It's not like Ellen can inherit the throne. I guess Queen Agatha was a bad judge of character, thinking her best friend will make a good mother to her daughter and wife to her husband.
I think the fact kings of marring wives must stop at a Young age of their kids, because IT does not feel good of being treated as trash đ even I overcome this situation with my step-fahter and half brother and sister