For first time in country’s history, a royal family member becomes directly involved in politics and runs for office.

Thailand’s King Maha Vajiralongkorn says his elder sister’s candidacy for prime minister is “inappropriate” and unconstitutional, likely ending her short political bid.

In an unprecedented move Friday, Thailand‘s Princess Ubolratana Rajakanya Sirivadhana Barnavadi announced she would run as prime minister in the country’s long-delayed general elections by Thai Raksa Chart, a party founded by allies of former Prime Minister Thaksin Shinawatra.

The registration of the king’s elder sister as a candidate marked the first time in the country’s history that a member of the royal family would become directly involved in politics and run for office.

The king in a palace statement said, “Involvement of a high-ranking member of the royal family in politics, in whatever way, is an act that conflicts with the country’s traditions, customs, and culture, and therefore is considered extremely inappropriate.”

His opposition is likely to lead to her disqualification by the Election Commission.

The princess was stripped of her royal title when she married a US national in 1972. She returned to Thailand in the late 1990s after getting a divorce. Although her formal title was not restored, she is regarded and treated as royalty by people in Thailand.

In a post on Instagram, Ubolratana said she was exercising her rights as a citizen in accepting Thai Raksa Chart’s nomination.

“I have relinquished my royal titles and lived as a commoner,” she said. “I have accepted the Thai Raksa Chart Party’s nomination for prime minister to show my rights and freedom without any privileges above other fellow Thai citizens under the constitution.”

Known to the public for lead roles in Thai films, Ubolratana is a long-time friend of the Shinawatra family, which has an influence on the March 24 election through its proxy political parties.

The Shinawatra family has not fielded a family member directly this time.

“The unpredictable nature of Thai politics just went up another level,” Al Jazeera’s Wayne Hay, reporting from Thailand’s capital, Bangkok, said.

“This has never happened before in Thai politics; the royal family has always been seen as being above politics even though everyone knows that it’s the most powerful body in Thailand.”

A small pro-military party, the People’s Reform Party, asked the Election Commission to consider whether the princess’s candidacy violated laws forbidding parties from invoking the monarchy in campaigns.

The Election Commission is required to endorse or reject all candidates by next Friday.

Separately, Prayuth Chan-ocha, the head of Thailand’s military government, said in a statement on Friday he would also contest the elections as a prime ministerial candidate for the pro-army Palang Pracharat party.

Prayuth is the army chief who seized power after the military toppled the administration of Yingluck Shinawatra, Thaksin’s sister, in a 2014 coup and made himself prime minister.

Princess Ubolratana is expected to be one of his main opponents.

Hay said Thaksin – who was also removed in a coup in 2006 – and Yingluck “have always been seen as being anti-establishment”.

“Their supporters and the supporters of the elite have clashed many times over the past decade, so to now come to this stage to have a member of the royal family running to be potentially the prime minister for a party backed by the Shinawatras is definitely an intriguing development for Thai politics.”

Thailand has been a constitutional monarchy since 1932 but the royal family has wielded great influence and commanded the devotion of millions.