Krom Phra Ratchawang Bowon Sathan Mongkhon กรมพระราชวังบวรสถานมงคล, colloquially known as the Front Palace, was the title of the uparaja of Siam, variously translated as "viceroy", "vice king" or "Lord/Prince of the Front Palace", as the titleholder resided in the physical residence of the same name. The office of Front Palace was considered second only to the king and regarded as the heir presumptive. The name, with its dual meaning, originated in the Ayutthaya period, and the holder later gained significant powers during the Rattanakosin period. Front Palace occupants were usually a son or brother of the reigning monarch. The office existed until the death of the last occupant, Prince Vichaichan, in 1885. King Chulalongkorn then abolished the office of an heir presumptive, introducing in its stead the Western concept of a crown prince as heir apparent, and styled the new office "Crown Prince of Siam".

The Ayutthaya Kingdom or the Empire of Ayutthaya was a Mon and later Siamese kingdom that existed in Southeast Asia from 1351 to 1767, centered around the city of Ayutthaya, in Siam, or present-day Thailand. European travellers in the early 16th century called Ayutthaya one of the three great powers of Asia. The Ayutthaya Kingdom is considered to be the precursor of modern Thailand, and its developments are an important part of the history of Thailand.