Paul Nghi, Pigneau avoided the Tay Son army in Cambodia, and came back to assist Nguyễn Ánh. They hid in the forest to avoid the pursuit of Tay Son army. Together, they escaped to the island of Pulo Panjang in the Gulf of Siam. Pigneau hoped that by playing a substantial role in a Nguyễn Ánh victory, he would be in position to lever important concessions for the Catholic Church in Vietnam, helping its expansion in Southeast Asia. In late 1777, the main part of the Tây Sơn army left Saigon to go north and attack the Trịnh lords, who ruled the other half of Vietnam. Nguyễn Ánh stealthily returned to the mainland, rejoining his supporters and reclaimed the city of Saigon. He was crucially aided by the efforts of Do Thanh Nhon, a senior Nguyễn Lord commander who had organized an army for him, which was supplemented by Cambodian mercenaries and Chinese pirates. The following year, Nhon expelled additional Tây Sơn troops from the surrounding province of Gia Dinh and inflicted heavy losses on the Tây Sơn naval fleet. Taking advantage of the more favorable situation, Nguyễn Ánh sent a diplomatic mission to Siam to propose a treaty of friendship. This potential pact, however, was derailed in 1779 when the Cambodians rose up against their pro-Siamese leader Ang Non II. Nguyễn Ánh sent Nhon to assist the revolt, which eventually saw Ang Non II defeated decisively and executed. Nhon returned to Saigon with high honor and concentrated his efforts on improving the Nguyễn navy. In 1780, in an attempt to strengthen his political status, Nguyễn Ánh proclaimed himself Nguyễn vương (Nguyễn king or Nguyễn ruler in Vietnamese) with the support of Nhon's Dông Sơn Army. In 1781, Nguyễn Ánh sent further forces to prop up the Cambodian regime against Siamese armies who wanted to reassert their control. Shortly thereafter, Nguyễn Ánh had Nhon brutally murdered. The reason remains unclear, but it was postulated that he did so because Nhon's fame and military success was overshadowing him. At the time, Nhon had much, if not dominant power, behind the scenes. According to later Nguyễn dynasty chronicles, Nhon's powers included that of deciding who would receive the death penalty, and allocating budget expenditures. Nhon also refused to allocate money for royal spending. Nhon and his men were also reported to have acted in an abrasive and disrespectful manner to Nguyễn Ánh.