Thailand is about to hold its prime minister election on March 24.

It will be the first election in almost five years in a country under military rule since a military coup in 2014.

The coup ousted a government led by former prime minister Thaksin Shinawatra’s sister, Yingluck Shinawatra.

Current prime minister Prayuth Chan-ocha was the Thai army chief who led the coup then.

But last week, something happened that upended all political norms in Thailand.

Bombshell announcement

Thai Princess Ubolratana Rajakanya, the elder sister of King Maha Vajiralongkorn, was nominated on Feb. 8 by Thai Raksa Chart Party to run for prime minister.

This party is one of the several that is closely linked to former populist Prime Minister Thaksin.

The development was unprecedented in Thai political history, and was so shocking that an analyst said it was “nowhere near” a 1,000 times of Brexit combined with Trump.

Shortly after, King Vajiralongkorn came out and opposed his sister's candidacy, declaring it "inappropriate" and "unconstitutional".

The election commission then disqualified her candidacy on Monday, Feb. 11, saying the royal family should be "above politics".

Here’s why Ubolratana’s decision to run for office is so controversial.

Thai monarchy is supposed to be separated from politics

The princess' nomination broke with a long-held tradition of members of the Thai monarchy staying above politics.

Thailand has been a constitutional monarchy for 86 years since 1932.

Most Thais revere the royal family, who holds immense influence among them.

Ubolratana, 67, is technically no longer a member of the royal family as she had relinquished most of her royal titles when she married an American whom she met while studying at the Massachusetts Institute of Technology (MIT) -- she graduated in 1973.

She currently holds the title "Daughter to the Queen Regent", that was bestowed upon her when she returned to Thailand after her divorce.

Nevertheless, she still performs her royal duties and is treated as a member of the royal family.

She had three children with her husband -- one of whom had passed away during the 2004 Indian Ocean tsunami.

In accepting a political party's nomination for prime minister, Ubolratana said in an Instagram post -- posted a few hours after her nomination was revealed -- that she was "exercising her rights and freedoms as a commoner".

Her popularity with Thais is evident as they are enamoured by her.

Possible solution to longstanding feud in Thai politics?

Thai politics has been divided by a 13-year-old feud between the royalists and military elites, known as the "yellow shirts", and Thaksin's supporters, known as the "red shirts".

The feud started when the military deposed Thaksin in a 2006 coup.

Since then, Thaksin has been living in self-imposed exile in Dubai, and still travels around the region, including coming to Singapore.

According to The Economist, although the March 24 election is theoretically supposed to restore democracy in the country, it might be a ruse by the military generals to preserve their influence and keep Thaksin out of Thai politics.

When Ubolratana's nomination first emerged, some thought that it was a plan cooked up by the royal family to unite the two rival factions and end the feud between them.

By having a royal to lead a party connected to Thaksin, the divide might then finally be bridged.

This is because not only is Ubolratana a friend of the Thaksins, she is also on good terms with her younger brother, who is king.

Therefore, she is in a strong position to gather support from both the "yellow shirts" and the "red shirts".

Furthermore, should Ubolratana's nomination be accepted, Prayuth, a staunch royalist, would presumably not stand against a royal candidate, according to The Economist.

Other than to end the conflict between the "yellow shirts" and "red shirts", Prayuth's coup back in 2014 was supposedly executed to protect the monarchy.

However, the King's opposition to his sister's candidacy strongly disproved this theory.

Here it goes again

While the princess' brief foray into politics appears to be over, another party connected to Thaksin, Pheu Thai, still remains in the race.

Brian Eyler, director of the Stimson Center's Southeast Asia programme, told CNBC:

"Thailand has long faced a cycle of Pheu Thai candidates winning elections, the military not accepting their tenure, a coup happening and then plans to return to democracy in which Pheu Thai candidates win again."

In facing off with the parties backing up the military, tensions between the "yellow shirts" and "red shirts" are set to heighten again.

Therefore, this short-lived episode might have done nothing but made the feud between the two warring factions worse.

Top image credit to MARTIN BUREAU/AFP/Getty Images