BANGKOK (THE NATION/ASIA NEWS NETWORK, REUTERS) - Former princess Ubolratana Rajakanya Sirivadhana Barnavadi posted a message on Saturday morning (Feb 9) to thank her supporters, but did not comment on her candidacy.

The older sister of King Maha Vajiralongkorn posted the message on her Instagram wall hours after the King prohibited her from standing in the upcoming election as a prime minister candidate of a party linked to ousted ex-premier Thaksin Shinawatra.

The 67-year-old former princess did not directly mention her brother or her political hopes, but thanked supporters for their "love and kindness toward each other over the past day" and expressed gratitude for their support for her.

"I would like to say once again that I want to see Thailand moving forward, being admirable and acceptable by international countries, want to see all Thais have rights, a chance, good living, happiness to all," she said, concluding with"#ILoveYou".

A political bombshell had been dropped on Friday morning when the Thai Raksa Chart party - an offshoot of the larger pro-Thaksin party that was ousted from power in the 2014 coup - nominated the 67-year-old as its sole candidate for prime minister in the upcoming elections.

But about 12 hours later, the King issued a nationally televised royal command saying immediate members of the Royal Family traditionally must stay above politics.

"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," the King said.

The King also cited a provision in the Constitution that states the monarch stays above politics and maintains political neutrality.

"All royal family members adhere to the same principles... and cannot take any political office, because it contradicts the intention of the Constitution."

The nomination of a royal family member by pro-Thaksin forces was an audacious gambit, potentially undercutting Thaksin's ardently royalist foes, and setting up an election showdown with Prime Minister Prayut Chan-o-cha, who led the 2014 coup and heads the military government.

But King Vajiralongkorn's swift rebuke of his sister's bid could backfire on pro-Thaksin forces, who could face retribution if judged by election authorities to have tried to illegitimately use a royal connection.

"Friday's events were astounding and have people completely rethinking their assessments and perspectives and the country's future political trajectory," said Mr Jay Harriman, senior director at BowerGroupAsia, a government affairs consultancy.

"The monarchy has semi-divine status in Thailand. Public appearances and statements often pertain to royal duty or events," he added. "A disagreement like this has almost never happened in recent memory."

In a statement on Saturday (Feb 9), Thai Raksa Chart expressed gratitude to the former princess and said it "accepts His Majesty's command with loyalty to the king and every single member of the royal family."

The party cancelled plans to launch election campaigns in Bangkok's China Town earlier on Saturday. It informed reporters without explanation that Thai Raksa Chart leader Preechaphol Pongpanit and party campaign chief Nattawut Saikaur would cancel the visit to Yaowarat.

Topping one of the most dramatic weeks in the nation's political history, Thailand's Election Commission said it will meet on Monday (Feb 11) morning, without specifying the agenda.

All parties contesting the election had to submit their candidate lists to the commission on Friday (Feb 8). It's supposed to check and validate the nominations by Feb 15.

While the Election Commission has the final say on approval of candidates, it seems unlikely its members would ignore the powerful influence of the king in making its decision.

Thailand has been a constitutional monarchy since 1932, but the royal family has wielded great influence.

Ms Ubolratana relinquished her royal titles in 1972 when she married an American, a fellow student at the Massachusetts Institute of Technology (MIT), Peter Jensen. She lived in the United States for more than 26 years before they divorced in 1998.