Thailand’s king has denounced the selection of his sister as a political party nominee for prime minister as "extremely inappropriate" and unconstitutional after the news sent shockwaves across the country.

Earlier Friday it had been announced Princess Ubolratana Mahidol, 67, was nominated as the prime ministerial candidate of the opposition Thai Raksa Chart Party, a party long thought to be opposed to the spirit of the monarchy.

POPULAR YOUTUBER FACES CHARGES AFTER CRITICIZING THAI PRINCESS’ DRESS

She will face off current Prime Minister Prayuth Chan-ocha, a leading candidate backed by the military, which is considered the backbone of the monarchy’s rule in the country.

But in an unusual step, King Vajiralongkorn released a statement after the announcement, saying such a move would "defy the nation's culture."

"Even though she has relinquished her royal titles in writing, she maintained her status and carried herself as a member of the Chakri dynasty," the king said in a statement read out on Thai networks.

"Involvement of a high-ranking member of the royal family in politics, in whatever way, is considered an act that defies the nation's traditions, customs, and culture, and therefore is considered extremely inappropriate."

The royal decree also said his sister's candidacy violated the constitution.

It is unclear if she will now be forced to withdraw her candidacy.

Prayuth led the 2014 military coup that removed Thailand’s last elected government. He accepted on Friday the nomination by the Palang Pracharat Party.

But Prayuth would be likely to have problems competing in an election against Ubolratana who will be viewed as the representative of the monarchy – the most respected and supported institution in Thailand – even though she lost her royal titles when she married an American more than four decades ago.

Thailand also has strict laws when it comes to the criticism of the monarchy, with sentences of up to 15 years in prison for defaming the royal family. The laws were also recently toughened to include any criticism of the royal institution, raising questions about how Prayuth will navigate the campaign without breaking the law.

THAI MONARCHY'S BILLIONS COME FROM REAL ESTATE, COMPANIES

Preechapol Pongpanit, the leader of the party that nominated the princess, earlier said that the party’s executive committee “agrees that Princess Ubolratana, who is intelligent and capable, is the most appropriate name.”

He added: “From my point of view, I think she understands Thai politics. She understands democracy.”

On Instagram, the princess released a statement saying she has “no special privileges above the Thai people under the constitution” and that she decided to take part in politics “out of sincerity and intention to sacrifice in this request to lead the country to prosperity.”

Thailand is a constitutional monarchy where the king and his immediate circle is barred from participating directly in politics.

CLICK TO GET THE FOX NEWS APP

But while the rules don’t ban political participation of distant relatives of the monarch, with some relatives of the family previously getting elected to the Parliament, Ubolratana appears to be a complex case as she’s commonly called and treated as a princess.

The Associated Press contributed to this report.