Who is Catalina who will become known as Katherine, Queen of Englan from The Constant Princess and what is their importance?

Catalina, later known as Katherine, Queen of England, is the daughter of Queen Isabella and King Ferdinand. At the age of three, she was engaged to Arthur, the prince of Wales and future King of England. When she grows up and travels to England, she is unable to adapt to her new home, seeing the people of England as barbarians at best.