While most people will tell you that London is one great big city, the truth is that there is one more London that it is inside of London.
The City of London situated within the city called London is actually the original London. However, to make things clearer, we need to go back nearly 2,000 years in history, to when the Romans invaded Britain and founded the settlement of Londinium.
Westminster was built nearby with the purpose of competing with the powerful City of London and this was when the second London was born. The new city expanded rapidly and it eventually surrounded the City of London. By 1889 the County of London was formed and the name was more often used for the larger area that surrounded the original City of London.
The City of London continued functioning independently, governed by a Corporation even after 1965, when the County of London and the County of Middlesex were abolished and Greater London was formed. The mayor of Greater London has nothing to do with the original City of London, which still has separate governing bodies and a mayor.
In fact, the City of London is so independent that it has its own flag, crest, police force, ceremonial armed forces, and a mayor who has a special title, the Right Honorable, the Lord Mayor of London. Oddly enough, if the monarch wants to enter the City of London, she first must ask the Lord Mayor for permission.