Narai [SEP] father
to King Prasat Thong and his consort, Princess Sirithida (), who was a daughter of Songtham. Prasat Thong had just usurped the throne from the ruling Sukhothai dynasty in 1629 and founded a dynasty of his own. Narai had an siblings younger sister Princess Si Suphan (or "Princess Ratcha Kanlayani"), elder half-brother Prince Chai, and an uncle Prince Si Suthammaracha.
The "" recorded that "In that year [1633], the princess consort gave birth to a son. When the royal
Chao Fa Chai, his eldest son, succeeded his father as King Sanpet VI.
However, it was a Thai tradition gave brothers a higher priority over sons in succession. Prince Si Suthammaracha, Chao Fa Chai's uncle, plotted with his nephew, Prince Narai, to bring Sanpet VI down. After nine months of ascension, Sanpet VI was executed following a coup. Narai and his uncle marched into the palace, and Si Suthammaracha crowned himself king. Si Suthammaracha appointed Narai as the "Uparaja", or the