2017
There is NO British Elizabeth III. The present reigning monarch is Elizabeth II.
The reigning Monarch, Queen Elizabeth II, is on the obverse of all British coins.
After Queen Elizabeth II's passing on September 8, 2022, her son, Charles III, ascended to the throne and became the reigning monarch. He is the first British monarch named Charles in over 300 years and has taken on a role that emphasizes continuity and modernization of the monarchy. His wife, Camilla, holds the title of Queen Consort.
In British Monarchy, there has not yet been a Queen Elizabeth III.
Elizabeth II recently celebrated (From the 2nd-4th of June 2012) her 60th Jubilee of her reign. She is still reigning but she began her duties in 1952. Before her, Queen Victoria ruled from 1837- 1900, 63 years. Finally, Elizabeth I ruled from 1558- 1603, 45 years. So to answer your question, Queen Victoria was the longest reigning British monarch but if Elizabeth rules into 2016, she will be bestowed this title.
Queen Elizabeth the second.
In British Monarchy, there has not yet been a Queen Elizabeth III.
In the British monarchy, the letters GR would stand for "George Rex", a Latin-like way of saying "George the King." Similarly, ER stands for Elizabeth Regina or "Elizabeth the Queen."
The monarchy is crumbling around our feet!
The reigning British monarch is on the obverse of all Australian coins. Currently, it is Queen Elizabeth II.
The President of the USA (or, indeed, any other nation) is the country's Head of State, whereas the British Prime Minister is not. He is the leading Minister of government, but Britain is a monarchy, so the Head of State is the reigning monarch, who at present is Queen Elizabeth II.
Elizabeth Bowes Lyon, known as the Queen Mother, was not a reigning queen but held the title of queen consort when her husband, King George VI, was on the throne. After his death in 1952, their daughter, Elizabeth II, became queen, making Elizabeth Bowes Lyon the mother of the reigning monarch. She was affectionately referred to as the Queen Mother to distinguish her from her daughter, the reigning queen, and to honor her significant role in British royal history.