Chetthathirat (Thai: เชษฐาธิราช) or Borommaracha II (บรมราชาที่ 2; c. 1613 – 1629) was the eldest son of King Song Tham and older brother of Athittayawong and Phra Srisin or Phra Phanpi Srisin (Thai: พระพันปีศรีศิลป์), all three of the House of Sukhothai. In childhood he was known as Chetthakuman (พระเชษฐากุมาร), meaning 'Chettha the Infant', or simply Chettha.

Chetthathirat reigned for a period of one year and seven months, after the death of his father, according to Songtham's wishes, and conveyed to Okya Sri Vorawong (Thai: ออกญาศรีวรวงศ์) or Phraya Siworawong – an influential royal page. The events were detailed by .

The king’s last wish, however, was objected to by some leaders in the kingdom, including the Kalahom Chaophraya Maha Senabodi. Siworawong gained supporters in the government, and even used the services of Yamada Nagamasa the Okya Senaphimok (Thai: ออกญาเสนาภิมุข). Upon king Songtham’s death, Chetthathirat took the throne and Siworawong arrested and executed those who had been opposed to the idea. The king was made Siworawong as Okya Kalahom Siworawong (Thai: ออกญากลาโหมสุริยวงศ์) or Chaophraya Kalahom.

Siworawong then induced Phra Srisin, who had entered the priesthood, to come to the palace with his followers. Siworawong captured him and ordered his execution. However, Chetthathirat spared his life but exiled him to Phetchaburi. Later Chetthathirat did execute Phra Srisin, when he plotted rebellion.

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