Corrected entry: The play this film is based on is called "The Madness of George III." Producers were keen to alter the name to include the word "King," to better get the nature of the film across. It's also theorized that outside of the U.K. a lot of audiences would assume it was a sequel if "III" remained as well, and despite protests by some people (who largely seem to assume that "outside of the UK" can only mean the USA, rather amusingly).
Corrected entry: During the final scene, when the outside of St. Paul's Cathedral is shown, the people are gathered around the statue of Queen Victoria, George III's grand-daughter, who was only born around 30 years later.
Correction: In front of St Paul's stands a statue of Queen Anne (r. 1702-1714), set up to celebrate the completion of the rebuilding of the cathedral within her reign. The original statue, the work of Francis Bird, was completed in finest Italian marble (1712). It suffered so badly in the sulphurous atmosphere of eighteenth-century London that it had to be replaced by the present replica (in Italian statuary marble) in 1886.
Correction: However amusing you find it to be, this drivel belongs in the same bin as the hanged Munchkin in 'The Wizard of Oz' and the ghost of the murdered boy in 'Thee Men and a Baby'. It's an urban myth. See http://www.snopes.com/movies/films/george.htm.