When his brother crowned himself as the king of Siam at Bangkok in 1781, he was appointed the Front Palace or Maha Uparaj, the title of the heir.

Bunma fled the city with a small carrack to join the rest of his family at Amphawa, Samut Songkram.

After the fall of Ayutthaya, the city and peripheral areas were under the control of the Burmese while local Siamese nobles established their own states.

After the establishment of Thonburi and coronation of Taksin, Bunma was appointed Phra Maha Montri (Royal Police of the Right).

In 1770, after the defeat of Lord Fang, Anuchitraja became Chao Phraya Surasi - the ruler of Phitsanulok and defender of northern frontiers.

From 1771 to 1781, Surasi joined his brother in massive campaigns subjugating the Laotian kingdoms of Vientiane, Luang Prabang, and Champasak, and Cambodia.

Maha Kasatsuek then crowned himself as Ramathibodi and moved the capital to the left bank of Chao Phraya river - modern Bangkok.

Maha Sura Singhanat led the Siamese forces to receive the Burmese attacks coming from the west and south.

However, Maha Sura Singhanat fell ill on the course of journey but dispatched his troops to Chiang Mai in substitution.