He is the only Danish monarch whose burial site is not known.

Currently, the Emperor of Japan is the only reigning monarch with the title.

Queen Elizabeth II is the only monarch of more than one independent nation.

He is the only American-born monarch in history.

In the finale, she asserts that Hong-hei is "the only righteous monarch."

Alfonso refused to abandon the siege but fell victim to the plague on 27 March 1350, becoming the only monarch to die of the disease.

He was the only medieval monarch to die of the plague.

George VI is the only reigning monarch to visit the island.

Frederick VII was the only monarch to live in the palace, between 1852 and 1863.

He is currently the only absolute monarch in Europe.