The older sister of the king of Thailand said Friday she will run for prime minister in elections next month, upending the palace's decades-long tradition of eschewing politics and setting up a surprise contest with the leading military-backed candidate.

Princess Ubolratana Mahidol's nomination by the opposition Thai Raksa Chart Party marks a shock realignment of Thai politics. The party is linked to former Prime Minister Thaksin Shinawatra, who hardcore royalists have long dismissed as opposed in spirit to the monarchy.

The nomination pits the princess against current Prime Minister Prayuth Chan-ocha, the preferred candidate of the military, considered one of Thailand's most royalist institutions.

Prayuth, who led the 2014 military coup that ousted Thailand's last elected government, on Friday also accepted his nomination as candidate for prime minister by the 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 the constitution and election rules implemented by his government make it difficult for political parties without military backing to capture the prime minister's post.

But Ubolratana's de facto alliance with the powerful political machine of exiled Thaksin, whose comeback the military has made every effort to block, puts Prayuth's supporters in an extremely awkward position. It will be difficult to block her political rise because she will be seen as a representative of the monarchy, the nation's most revered and respected institution.

Thailand also has a draconian lese majeste law which punishes defamation of the immediate royal family with up to 15 years in prison. While it does not technically apply to Ubolratana, who lost her highest royal titles when she married an American more than four decades ago, its scope has been widened in recent years to almost anything that sullies the royal institution, making criticism of the princess highly problematical.