Borommaracha Kasat Bowon Sucharit (Thai: บรมราชากษัตริย์บวรสุจริต), Somdet Phra Chao Yu Hua Phra Thi Nang Suriyat Amarin (Thai: สมเด็จพระเจ้าอยู่หัวพระที่นั่งสุริยาสน์อมรินทร์), Chaofa Ekathat (Thai: เอกทัศ), or Krom Khun Anurak Montri (Thai: กรมขุนอนุรักษ์มนตรี), was the 33rd and last monarch of Ayutthaya Kingdom, ruling from 1758 to 7 April 1767 prior to the fall of the kingdom. Moreover, he was called by the people at the time being that "Khun Luang Khi Ruan" (Thai: ขุนหลวงขี้เรื้อน), meaning "king with skin disease".
In 1759, Alaungpaya ordered his second son, Hsinbyushin, to attack Tenasserim and Mergui, telling Siam their friendship with Burma was ended since Siam refused to deliver a rebel Mon nobleman who had fled in a French vessel to Mergui. Meeting little resistance, the Burmese continued their advance by attacking other Siamese provincial towns. After capturing Phetchaburi, Alaungpaya decided to advance to Ayutthaya in 1760.
The Siamese capital was in confusion and an uproar after the Burmese had taken Ratchaburi. Ekkathat was forced to invite his abdicated brother, Uthumphon, to leave the priesthood and resume the sovereignty. Ekkathat became Somdet Phrachao Luang, "king who had abdicated his throne". Umthumphon then prepared the capital for a siege.
However, Alaungpaya was wounded during the siege, and died during the Burmese retreat.
This postponed the death of Ayutthaya for another 7 years.
Siam under Ekkathat was in turmoil. Ayutthaya lost its control over network cities and Ekkathat was said to be indulged by the luxury of the court and concubines. The peasants went on the rebellion. In 1766, the Burmese armies again invaded Siam—through Mergui under Mahanoratha and Lanna under Neimyo Thihapate after subjugating Lanna and Laotian kingdoms. The Burmese captured various peripheral cities to cut down any supports given to Ayutthaya. A Dutch source said the court faced bankruptcy. The capital totally lost contact with its satellite. Ayutthaya was then helpless.
Local accounts told that Ekkathat desperately tried to counter the Burmese. He ordered his remaining armies and fleets to counter the Burmese at Ratchaburi and Thon Buri, but the Burmese crushed them all. The two Burmese armies joined at Ayutthaya and laid the siege on the city. A foreign account claimed that Ekathat and his family secretly fled from the capital. The nobles then agreed to surrender. On April 7, 1767, Ayutthaya fell. The Burmese looted and burnt the city to the ground.
Siamese chronicles said Ekkathat died upon having been in starvation for more than ten days while concealing himself at Ban Chik Woods (Thai: ป่าบ้านจิก), adjacent to Wat Sangkhawat (Thai: วัดสังฆาวาส).