Borommakot (Thai: บรมโกศ) or Borommarachathirat III (Thai: บรมราชาธิราชที่ 3) was the king of Ayutthaya from 1733 to 1758. His reign was the last blooming period of Ayutthaya as the kingdom would fall nine years after his death.
"His reign of 25 years is important for being the last peaceful period of Ayudhya during which literature with the arts and crafts flurished." However, the king himself was known for "cruelty to people and animals alike," with seven of his sons meeting violent deaths.
In 1741, Borommakot made his son Thammathibet the Front Palace. Thammathibet proved to be an able prince and was a poet. However, Thammathibet had affairs with two of Borommakot's concubines, Princess Sangwan and Princess Nim - a severe crime. The lovers were caught in 1746 and the three were beaten. The Front Palace was lashed 120 stokes and the two concubines 30 each. The Front Palace died while he was beaten and Princess Sangwan died 3 days later. Princess Nim survived, but she was banished from the court.
Borommakot then appointed his third son, Duea (เดื่อ; later became Uthumporn), as the Front Palace. Borommakot skipped his second son, Ekkathat, because he thought that Ekkathat was not suitable to be a king.
However, Ekkathat still had designs on the throne, and the subsequent struggles of the princes for the throne would contribute to the fall of Ayutthaya in 1767, during the reign of Ekkathat.