Chim was born in 1767 during the
Ayutthaya Kingdom in
Amphawa District, Samut Songkram. He was a son of Luang Yokkrabat of
Ratchaburi and Nak of Samut Sakorn, as his father and mother were then known. They would later become King
Rama I and Queen
Amarindra, respectively. In 1767, Ayutthaya fell to
Konbaung Burmese invaders. His father, Phraya Ratchaburi, joined
Taksin's forces to recapture the city. Under King Taksin, Chim's father rose rapidly to high rank as a military leader and was assigned with the campaigns to subjugate
Laos and
Cambodia. In 1782, his father crowned himself King of Siam (later named Rama I) and Chim himself was raised to the title of
Prince Itsarasunthon of Siam. Itsarasunthon with his concubine
Riam (later elevated to Princess Mother Sri Sulalai by her own son), fathered Prince Thap ( – later
Rama III) in 1787. Prince Itsarasunthon then had a secret affair with his own cousin, Princess
Bunrot. In 1801, Rama I then found out that Princess Bunrod had been pregnant for four months and banished her out of the palace to live with her brother. Itsarasunthon, however begged his father to forgive him and the princess was reinstated and became his consort through the negotiation by concubine
Khamwaen. Unfortunately, the baby died just after its birth. With Princess Bunrot, Itsarasunthon also fathered
Mongkut (1804) and
Pinklao (1808). His other concubine, namely Prang Yai, gave birth to Prince
Wongsa Dhiraj Snid (Nuam) in 1808. He also married his agnatic half sister, Princess
Kunthon Thipphayawadi. They had three sons: Prince Abhorn (1816), Prince Klang (1819), and Prince Piu (1822). Later, Prince Klang would be known as Prince Mahamala. He was granted the title of
Krom Khun Bumraap Porapuksa, the 4th
level of Krom ranks by Mongkut then elevated to
Krom Phraya by
Chulalongkorn. Prince Itsarasunthon was appointed to the
Front Palace as Lord of the Front Palace or
Uparaja in 1807 to succeed his uncle
Maha Sura Singhanat who had died in 1803, though he continued to stay at the Thonburi Palace. The King had 83 children. Among his many other children was Prince
Wongsa Dhiraj Snid (born Prince Nuam), who was a royal physician for many years as well as a field commander and diplomat. ==Ascension==