A Thai political party’s stunning decision to nominate the king's sister as its candidate for Prime Minister backfired when the monarch forbade her to do so. The party has now sworn loyalty to the king and thanked his sister for her effort.

Thailand woke up on Saturday with a political hangover, pondering why Princess Ubolratana Mahidol agreed on Friday to be a candidate for the Thai Raksa Chart Party — breaking with tradition proscribing the monarchy's involvement with politics. Before the day was over, King Maha Vajiralongkorn invalidated the action, calling it 'inappropriate' and unconstitutional.

The selection of Ubolratana by the Thai Raksa Chart Party would have tied the king's eldest sister to the political machine of former Prime Minister Thaksin Shinawatra, which hardcore royalists have long dismissed as opposed in spirit to the monarchy.

She would have been pitted against the preferred candidate of the pro-royalist military, Prime Minister Prayuth Chan-ocha, who led the 2014 ouster of an elected government.

Prayuth had been considered the front-runner for the March 24 polls because changes in constitutional law and election rules were implemented by his government in a manner making it difficult for political parties without military backing to capture the premier's post.