The Coup
In the end, the Coup Group chose to disregard Phibun as well as the king. On November 26 they sent a representative to the prime minister to suggest reverting the 1949 constitution to the less democratic and anti-royalist one of 1932. The proposal was immediately rejected by Phibun, but, three days later, nine leading members of the Coup Group - among them Phao Siyanon, Field Marshals Phin Chunhawan and Sarit Thanarat, and Air Chief Marshal Fuen Ronnaphakat - pressed him in person. Phibun again angrily rebuffed them, but by then the Coup Group was getting desperate. The king planned to return from Lausanne in two days to resume his royal duties and the generals could not risk a dangerous confrontation with the monarch. Therefore that evening, while the king was en route from Singapore to Bangkok, they announced over the radio the dissolution of parliament, reinstatement of the 1932 constitution, and formation of a provisional government. Phibun initially refused to join the new government but, after much negotiating, accepted the fait accompli. The next morning he signed on again as prime minister.
Read more about this topic: Silent Coup (Thailand)