Source: Thailand Royal Office
Nicknamed "Koi", Ms Sineenat was condemned Monday in a royal command aired on national television for "acting against the appointment of the queen".
On Wednesday six high-ranking palace officials were fired, including "a nurse at the bedroom guard service" and a veterinarian, according to two separate announcements released by palace mouthpiece the Royal Gazette.
"They have severely breached disciplinary conduct for their evil actions by exploiting their official positions for their own or other people's gain," said the gazette.
Thailand's royal family is protected by a draconian defamation law that makes scrutiny of it, or debate over its role, almost impossible inside the kingdom.
The public is often able to glean clues to the inner workings of the palace through its use of symbolic imagery and the fates of royal aides.
Ms Sineenat, who has not been seen in public since Monday, has been trending on Thai social media with the hashtag #SaveKoi.
Source: ROYAL HOUSEHOLD BUREAU
King Vajiralongkorn ascended the throne in 2016 following the death of his beloved father, who was regarded by Thais as a figure of moral authority.
Josh Kurlantzick from the US-based Council of Foreign Relations said his decision to strip his consort of her title was part of a broader push for power.
"I think it's just one of many moves that he has done that shows he's consolidating power in a wide range of ways including some that seem a little bit personal.
"It goes with a whole range of other moves that shows he doesn't want to have any restraints on his power, as well being a little vindictive."
During his reign so far, King Vajiralongkorn, also known by the title King Rama X, has moved to consolidate the authority of the monarchy, including taking more direct control of the crown's vast wealth and transferring two military units to his personal control.
He also reintroduced the "Ratchasawat," a basic code of conduct for those in royal service rooted in the old absolutist court, and has punished royal staff who have breached this code in the past.
King Vajiralongkorn, 67, had been married three times when he was the Crown Prince before ascending the throne.
In 2014, he divorced his third wife, former lady-in-waiting Srirasmi Suwadee, after the arrest of several of her relatives in an investigation into people making false claims of having links to the monarchy for financial gain.
Her uncle, parents and three brothers were later convicted of lese majeste and remain in prison.
Ms Suwadee, who was never charged herself, lives outside Bangkok and has rarely been seen in public since the divorce.