The Mad King

The Mad King by Edgar Rice Burroughs

Ruritanian adventure from the author of Tarzan
Set in the fictional European kingdom of Lutha, this is the story of a young American Barney Custer, who is the son of an American farmer and a runaway Luthan princess, Victoria Rubinroth. Unaware of his royal blood, much less that he is the spitting image of his relative Leopold, the current king of Lutha, Barney visits Lutha on the eve of the First World War to see for himself his mother's native land. As he arrives in Lutha, King Leopold has just escaped from his ten years' imprisonment at the hands of his scheming uncle, Prince Peter of Blentz. Much to his own and everyone else's confusion, Barney is naturally mistaken for the king, leading to numerous complications and of course classic swashbuckling adventure.

Edgar Rice Burroughs (1 September 1875 – 19 March 1950) was an American writer, best known for his prolific output in the adventure, science fiction, and fantasy genres. Best-known for creating the characters Tarzan and John Carter, he also wrote the Pellucidar series, the Amtor series, and the Caspak trilogy.
After the war ended, Burroughs moved back to Encino, California, where after many health problems, he died of a heart attack on 19 March 1950, having written almost 80 novels. He is buried in Tarzana, California, US.
At the time of his death, he was believed to have been the writer who had made the most from films, earning over $2 million in royalties from 27 Tarzan pictures.
The Science Fiction Hall of Fame inducted Burroughs in 2003