The Royal Gazette published an announcement, just days before the king's coronation, saying Suthida Vajiralongkorn na Ayudhya, a former flight attendant, had "legally married" the king in accordance with royal traditions.

"Therefore, he bestows (the title) on General Suthida Vajiralongkorn na Ayudhya from Queen Consort to Queen Suthida as of now," the announcement said.

The ceremony was overseen by Vajiralongkorn wearing a white uniform in Bangkok's Dusit Palace Wednesday, according to a broadcast of the announcement, which showed Queen Suthida in a traditional Thai silk dress.

The unpredictable king is due to be crowned the 10th monarch of the Chakri dynasty in an elaborate three-day ceremony starting Saturday.

Long seen trailing the king in public events as part of his personal security retinue, Suthida, a former Thai Airways flight attendant, was given the rank of "general" in 2016.

Vajiralongkorn, who has been married three times, is frequently abroad in Germany.

Harsh lese-majeste laws have shielded public scrutiny of his colourful private life, and all media in Thailand must self-censor.

This weekend's coronation will be the first since Vajiralongkorn's late father's nearly 70 years ago.

It was not immediately clear what role Queen Suthida will play in the ceremony.