After the death of his father in 1709 Prince Phet was crowned as King of Siam and took the reigning name Phumintharacha (Thai: ภูมินทราชา).

[4]: 67 In the early reign of King Thai Sa, there was a royal succession conflict in Cambodia.

In 1715, Nguyễn Phúc Chu the Nguyen lord (Vietnam) who supported King Kaev Hua III invaded Oudong and King Thommo Reachea III and Prince Ang Tong along with their families fled to Ayutthaya for protection.

Prince Phon, the younger son of Sanphet VIII managed to defeat his nephews and took the throne as King Borommakot.

[2]: 280–281 As it appears in the archives of the French bishopric coming in Ayutthaya time by Adrien Louney that he has an abscess in his mouth or throat, while in the Autthaya Chronicle by Chat, Phra Chakkraphatphong it was recorded that he had a tongue disease.