In 1931, an ex-policeman challenged King George V for the throne of England. Needless to say, he lost.
Anthony Hall argued that he was the 23rd descendent of Henry VIII and tried to convince mass crowds at a series of public meetings in the Birmingham Bull Ring that he was rightful heir to the throne. He started raising eyebrows in Whitehall and Buckingham Palace after making “scurrilous” attacks on the King, including a threat to shoot him.
Hall traced his ancestry to Thomas Hall, the bastard son of Henry VIII, who died in 1534. He also claimed that James I of England was a changeling and could not have been the son of Mary, Queen of Scots, because he was “goggle-eyed”, his head was too large for his body, his tongue too large for his mouth and his legs were so rickety that he could not ride. [Link]"King Anthony" was rounded up and subjected to psychiatric tests, but passed with flying colors. He was later convicted of disturbing the peace and fined £10.
A novel published last year, Heir Unapparent, took up Anthony's cause, but the last time I checked the Windsors still hadn't vacated the premises.