 When King Songtham died in 1628, Chetthathirat ascended the throne and a great purge of the mandarins who had supported Phra Sisin was instigated, including the "Samuha Kalahom" or Defence Minister.Prasatthong then replaced him as the defence minister with the new title of "Okya" Suriyawong ().During the King Chetthathirat’s reign, Prasat Thong had Yamada Nagamasa, the head of Japanese mercenaries then known as "Okya" Senaphimok (), as a supporter.