Catherine de' Medici (a very realistic portrait of her which shows, why her contemporaries described her as a very beautiful woman).yes, this is Catherine de' Medici you've watched on Reign, former Queen of France
Very similar to another portrait I'm studying (Eleanora (Dianora) di Garzia de Medici) but I have no attribution information for this image. The colors of the undergowns are similar as well as the details of the partlet, sleeves, jewelry, etc.
By Michael Sittow. A young Catherine of Aragon, known at this age for her beauty. Daughter of Ferdinand and Isabella of Spain, wife to Prince Arthur of England and, more famously, to his younger brother Henry VIII.