[3] Enticed by the Greek Constantine Phaulkon, he returned to France to suggest an alliance with the king of Siam Narai to Louis XIV.

The mission was led by Simon de la Loubère and Claude Céberet du Boullay, director of the French East India Company.

The disambarkment of French troops in Bangkok and Mergui led to strong nationalistic movements in Siam directed by Phra Petratcha and ultimately resulted in the 1688 Siamese revolution in which king Narai died, Phaulkon was executed, and Phra Petratcha became king.

[8] Meanwhile, Tachard returned to France with the title of "Ambassador Extraordinary for the King of Siam", accompanied by Ok-khun Chamnan, and visited the Vatican in January 1688.

He met with Kosa Pan, now Minister of Foreign Affairs and Trade, and the new king Petracha, but the meeting remained purely formal and led to nothing.