Rex is the term for king ie george V rex
Queen Victoria was known as Victoria Regina because "Regina" is Latin for "queen," and it was a common practice for British monarchs to use this title. This Latin term was added to the end of Victoria's name to emphasize her status as queen and to distinguish her from other individuals with the name Victoria.
The Queens surname is not Regina Rex. Regina is the Latin term for Queen and Rex the Latin for King. Hence her insignia shows ER, Elizabeth Regina or Queen Elizabeth. The same insignia is used for the King, thus if Prince Charles were to be King and he took the name Charles his would be CR, Charles Rex or King Charles. The Queens insignia also has the Roman Numerals II, acknowledging she is Queen Elizabeth the 2nd.
King and Queen.
The term for a colony under the direct control of the Queen or King was a kingdom. There were also parts of a kingdom called Principalities.
Shaba-naba :) And for queen is scabnar