25 Cents

Redonda is an uninhabited Caribbean island claimed by Antigua and Barbuda, with no government, no permanent population, and no monetary system. Its "kingdom" title derives from a 19th-century literary eccentricity — the writer M.P. Shiel declared his father king in 1880, and the title has passed through a succession of British authors ever since. Coins issued in its name are fantasy pieces with no circulation history and no issuing authority in any recognized sense.

The X# prefix in Krause's catalog places this squarely in the "unusual world coins" section, alongside other privately issued non-circulating novelties.