Thai Princess Ubolratana Mahidol accepted her nomination by the Thai Raksa Chart Party in an Instagram post. Hours later, Thailand's King called her candidacy "inappropriate and unconstitutional" and vetoed the move.
Thailand's king has issued an order stating that no member of the royal family should be involved in politics, quashing a bid by his older sister to run for prime minister in next month's elections.
An order issued by King Maha Vajiralongkorn read out on national TV late Friday night said his sister's candidacy was inappropriate and violated the constitution's intent.
Princess Ubolratana Mahidol's nomination earlier on Friday by an opposition party had upended politics in Thailand and threatened the palace's decades-long tradition of eschewing political involvement.
Because Thailand is a constitutional monarchy, the king and his immediate circle are not supposed to involve themselves directly in politics.
Many Thais had assumed that the princess would not have sought the nomination without her brother's blessing and were surprised that he would have supported her association with a party that is considered unsympathetic to the monarchy.
The selection of Ubolratana by the Thai Raksa Chart Party marked a shock realignment of Thai politics by tying 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.
Ubolratana accepted the nomination on Instagram, saying she was exercising her rights as a citizen with the move.
It had pit her against the preferred candidate of the military, which is considered one of Thailand's most royalist institutions.
Ubolratana relinquished her royal titles in 1972 after marrying an American fellow student, but she is still treated by officials and the Thai public as a member of the royal family.
The Election Commission is required to endorse or reject all candidates by next Friday.
TRT World 's Natasha Hussein reports.
Current Prime Minister Prayuth Chan-ocha, who led the 2014 coup that ousted Thailand's last elected government, on Friday accepted his selection as a candidate to lead the next government by Palang Pracharat Party, widely seen as a proxy for the military.
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.
Ubolratana was not present when her name was registered with the Election Commission by the Thai Raksa Chart Party. Its leader, Preechapol Pongpanit, said its executive committee "agrees that Princess Ubolratana, who is intelligent and capable, is the most appropriate name."
"From my point of view, I think she understands Thai politics. She understands democracy," he told reporters.
Ubolratana, 67, is the first-born of four children of the late King Bhumibol Adulyadej and Queen Sirikit, with the current king the second-born.
She was virtually disowned by her father in 1972 when she married an American who was a fellow student at the Massachusetts Institute of Technology. They settled in the United States where she and her husband, Peter Jensen, had three children. Only after a divorce did she move back permanently to Thailand in 2001.
She experienced tragedy, losing her autistic son Poom to the 2004 Asian tsunami.
She is also known to the public for lead roles in Thai films, onstage singing performances, a vibrant fashion sense and a sizeable Instagram following.
Since then she has thrown herself into charity work, especially her "To Be No. 1" foundation to fight youth drug abuse. She also frequently promotes Thai tourism and movies at international forums. In general, like most of the royal family, she publicly kept herself aloof from Thailand's recent political turmoil.
From Bhumibol to Thaksin
For most of Bhumibol's reign from 1946 to his death in 2016, the revered and humble monarch was a stabilising force in Thai politics. But the election of the telecommunications tycoon Thaksin in 2001 was transformative for Thailand.
His populist policies delivered unmatchable electoral majorities, but he was resented by the traditional ruling class, including royalists and the military. Violent street protests and two military coups have marked the years since. Thaksin went into exile in 2008 to avoid serving jail time on a corruption conviction he insists was politically motivated.
His well-funded political machine returned his allies to power twice, and his manoeuvring is seen as the key element in arranging for Ubolratana's selection by a Thaksin-affiliated party.
Most observers of Thai politics agree that Thaksin aggressively pursued good relations with Ubolratana's brother, current King Maha Vajiralongkorn, and friendship with the princess herself. These links were formed as royalists and others loyal to Bhumibol accused Thaksin of showing disrespect for the throne, and even of harbouring secret republican tendencies.
Thai Raksa Chart Party chief Preechapol brushed aside questions about Thaksin.
"I don't think that Khun (Mr) Thaksin will be involved about this," he said. "I don't think it's appropriate to talk about a third person."