In the novel The Secret of Chimneys, Nicholas IV was the last king of Herzoslovakia. He fell in love with a common Parisien actress Angèle Mory and married her, making her "Queen Varaga". The woman was totally unacceptable to the people of Herzoslovakia. Although the King forced his ministers to accept the marriage, the people rose up in revolution and assassinated the king. With the death of the king, his heir would have been one Prince Nicholas who was rumoured to have died in the Congo.
Sometime before the revolution, King Nicholas IV and his queen were guests of Lord Caterham at "Chimneys". Much of the intrigue in the story concerns the consequences of this visit.