Which British monarch of the 20th century was not crowned?
Edward VIII (born Edward Albert Christian George Andrew Patrick David, 23 June 1894 – 28 May 1972) was King of the United Kingdom, from 20 January 1936 until 11 December 1936.
Edward abdicated (resigned) from the throne, because he wanted to marry the American Wallis Simpson. Simpson had been married twice before. As King, he was Head of the Church of England, and the Church did not support divorce. After abdicating as king, he was known as His Royal Highness the Duke of Windsor. His wife was not allowed to be called "Her Royal Highness".
Due to his abdication he never had a coronation and therefore was never crowned King of the United Kingdom.