A political party in Thailand has been forced to disband after nominating the king’s sister as its candidate for prime minister.

Members of the Thai Raksa Chart Party’s executive board were also banned from political activity for 10 years by the Constitutional Court.

The court ruling raised fresh questions about the fairness of the upcoming general election on 24 March – the first since the military took over the country in a coup five years ago.

The Thai Raksa Chart Party, backed by exiled ex-prime minister Thaksin Shinawatra, nominated Princess Ubolratana Mahidol as its candidate for the upcoming election.

But her brother King Maha Vajiralongkorn issued a royal order calling the nomination highly inappropriate and unconstitutional the same day it was announced.

Thailand's transgender candidate Show all 6 1 /6 Thailand's transgender candidate Thailand's transgender candidate transgender2.jpg In this Thursday, Feb. 14, 2019, photo, Pauline Ngarmpring poses for a photograph at the Mahachon party head office in Bangkok, Thailand. As Pinit Ngarmpring, he was a CEO and sports promoter, well known in the world of Thai soccer. Now, under her preferred new name of Pauline Ngarmpring, she's pursuing a bid to become the country's first transgender prime minister. (AP Photo/Gemunu Amarasinghe) (AP Photo/Gemunu Amarasinghe) Thailand's transgender candidate transgender3.jpg In this Wednesday, Feb. 13, 2019, photo, Pauline Ngarmpring, a transgender person and a prime minister candidate in the upcoming Thai general election, speaks during an interview with The Associated Press in Bangkok, Thailand. As Pinit Ngarmpring, he was a CEO and sports promoter, well known in the world of Thai soccer. Now, under her preferred new name of Pauline Ngarmpring, she's pursuing a bid to become the country's first transgender prime minister. (AP Photo/Gemunu Amarasinghe) (AP Photo/Gemunu Amarasinghe) Thailand's transgender candidate transgender4.jpg In this Wednesday, Feb. 13, 2019, photo, Pauline Ngarmpring, right, a transgender person and a prime minister candidate, and Namklenginarin, center, a candidate for the parliament, both representing the Mahachon party for the upcoming Thai general election, greet people during an election campaign in Bangkok, Thailand. As Pinit Ngarmpring, he was a CEO and sports promoter, well known in the world of Thai soccer. Now, under her preferred new name of Pauline Ngarmpring, she's pursuing a bid to become the country's first transgender prime minister. (AP Photo/Gemunu Amarasinghe) (AP Photo/Gemunu Amarasinghe) Thailand's transgender candidate transgender5.jpg In this Wednesday, Feb. 13, 2019, photo, A transgender person and a prime minister candidate Pauline Ngarmpring, center, and house candidate Namklenginarin, right, both representing the Mahachon party for the upcoming general election, greet people during an election campaign in Bangkok, Thailand. As Pinit Ngarmpring, he was a CEO and sports promoter, well known in the world of Thai soccer. Now, under her preferred new name of Pauline Ngarmpring, she's pursuing a bid to become the country's first transgender prime minister. (AP Photo/Gemunu Amarasinghe) (AP Photo/Gemunu Amarasinghe) Thailand's transgender candidate transgender6.jpg In this Wednesday, Feb. 13, 2019, photo, Pauline Ngarmpring center, a transgender person and a prime minister candidate of the Mahachon party for the upcoming general election, greets people during an election campaign in Bangkok, Thailand. As Pinit Ngarmpring, he was a CEO and sports promoter, well known in the world of Thai soccer. Now, under her preferred new name of Pauline Ngarmpring, she's pursuing a bid to become the country's first transgender prime minister. (AP Photo/Gemunu Amarasinghe) (AP Photo/Gemunu Amarasinghe) Thailand's transgender candidate transgender1.jpg In this Wednesday, Feb. 13, 2019 photo, Pauline Ngarmpring, left, speaks with workers of a roadside massage parlor during an election campaign in Bangkok, Thailand. As Pinit Ngarmpring, he was a CEO and sports promoter, well known in the world of Thai soccer. Now, under her preferred new name of Pauline Ngarmpring, she's pursuing a bid to become the country's first transgender prime minister. (AP Photo/Gemunu Amarasinghe) (AP Photo/Gemunu Amarasinghe)

As legal justification for the nomination, the party pointed out that Princess Ubolratana held no formal royal titles because they were rescinded when she married an American in 1972.

But a nine-judge panel rejected this and instead followed the king’s line of argument that “even though she relinquished her title according to royal laws...she still retains her status and position as a member of the Chakri dynasty”.

Reacting to the ruling, Princess Ubolratana said the decision to dissolve the party was “sad and depressing” in response to a comment on her Instagram account.

Thai Raksa Chart leader Preechapol Pongpanit said: “I and the party’s executives have the utmost regret over the party’s dissolution, which affects the fundamental political rights and freedom of the party members and the people.”

He added: “For me and the party executives, no matter what our status is, we will act for the benefit of the country.”

The Constitutional Court has consistently ruled against Thaksin and his allies, whose parties have won every national election since 2001 but have twice been toppled in coups.

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Thaksin went into exile in 2008 to avoid serving jail time on a corruption conviction he insists was politically motivated.

His populist policies delivered unmatchable electoral majorities, but he was resented by the traditional ruling class, including royalists and the military.