Here are the key personalities in the events following a Thai political party's bid to have a former princess as its prime ministerial candidate, and the key players in the upcoming elections.
KING MAHA VAJIRALONGKORN, 66
Formally known as Rama X of the Chakri dynasty, the King ascended the throne following his father King Bhumibol Adulyadej's death in October 2016.
He has since reorganised palace affairs, bolstering his own security detail and granting himself personal stewardship of the multibillion-dollar crown assets.
He will officially be crowned King in a ceremony from May 4 to 6.
FORMER PRINCESS UBOLRATANA RAJAKANYA, 67
The elder sister of King Maha Vajiralongkorn was nominated as the prime ministerial candidate of Thai Raksa Chart Party, only for her bid to be stymied by her brother, the King, some 13 hours later.
In a world of strict decorum that defines Thai royal life, she stands out for her accessibility - she is an actress and singer, and replies to queries from the more than 97,000 followers of her Instagram account.
PRAYUT CHAN-O-CHA, 64
The current prime minister and former army chief led a 2014 coup that ousted a civilian government to end a prolonged period of sometimes deadly unrest.
A staunch royalist and an opponent of former premier Thaksin Shinawatra, Mr Prayut accepted the nomination of pro-military Palang Pracharath Party to be its prime ministerial candidate in the upcoming elections.
THAKSIN SHINAWATRA, 69
The former prime minister was ousted in a 2006 coup and has since lived in self-imposed exile to avoid a conviction in 2008 for violating conflict of interest rules, which he says was politically motivated.
Despite his legal troubles, Thaksin is still immensely popular with voters from the country's rural north and north-eastern provinces due to his previous populist policies.