Rama IV is crowned King of Thailand after the death of his half-brother, Rama III.

Mongkut was the fourth king of Siam from the Chakri dynasty, titled Rama IV. He reigned from 1851 until his death in 1868.

The monarchy of Thailand is the constitutional form of government of Thailand. The king of Thailand is the head of state and head of the ruling Chakri dynasty.

Thailand, is a country in Southeast Asia on the Indochinese Peninsula. It is officially the Kingdom of Thailand and historically known as Siam, the official name until 1939. With a population of almost 66 million, it spans 513,115 square kilometres (198,115 sq mi). Thailand is bordered to the northwest by Myanmar, to the northeast and east by Laos, to the southeast by Cambodia, to the south by the Gulf of Thailand and Malaysia, and to the southwest by the Andaman Sea; it also shares maritime borders with Vietnam to the southeast and Indonesia and India to the southwest. Bangkok is the state capital and largest city.

Nangklao, also known by his regnal name Rama III, was the third king of Siam from the Chakri dynasty, ruling from 21 July 1824 to 2 April 1851.

April 3 is the 93rd day of the year in the Gregorian calendar; 272 days remain until the end of the year.