Former Prime Minister Thaksin Shinawatra was formally indicted on Tuesday on a charge of insulting Thailand's monarchy, prosecutors announced at a news conference.
Thaksin reported himself to prosecutors just before 9 a.m. local time (0200 GMT) and the indictment process had been completed, Prayuth Bejraguna, a spokesperson for the Office of the Attorney General, said.
A series of high profile political legal cases are running concurrently in Thailand this week and putting in sharp focus the judiciary's impact on politicians and political parties in 2024.
Back to Thailand, jailed, pardoned, now indicted again
Thaksin, 74, was prime minister from February 2001 to September 2006.
Despite being ousted from power 18 years ago, Thaksin remains an influential figure in Thai politics, as does the Pheu Thai Party tied to him. He only recently returned to Thailand after years abroad.
After his years in self-imposed exile, he came back last year and started serving a separate jail term of more than eight years on charges related to corruption and abuse of power.
He was subsequently granted a royal pardon and released early on parole in February.
Thai lese majeste rules among world's most strict
The comments in question stem from a 2015 interview given in South Korea, shortly before the death of Thailand's previous King Bhumibol Abdulyadej and soon before his son Maha Vajiralongkorn took the throne.
Thailand is one of a few remaining countries to still criminally prosecute perceived insults or defamation of royalty. Each count can carry a maximum sentence of 15 years.
Several high-profile Thai political court cases moving this week
As well as the investigation into Thaksin, Thailand's Constitutional Court is also hearing a case lodged by a group of senators that could potentially lead to the dismissal of Prime Minister Srettha Thavisin. He's accused of breaching the law by appointing a lawyer with a conviction to his Cabinet.
The same court is hearing a case seeking to disband the popular opposition Move Forward Party for its campaign to amend the country's royal insult law. This follows a complaint from the national election commission.
And the court is also set to rule on whether the ongoing selection of members for the upper house of parliament, which started this month and is set to conclude in July, is lawful.
Investors have responded negatively to the cases, with Thailand's main stock index dropping to its lowest level since November 2020 in Monday's trading.