Bangkok — Thailand's Princess Bajrakitiyabha Mahidol, a lawyer and the eldest of King Maha Vajiralongkorn's children, has died at 47, the Bureau of the Royal Household said.

She died Thursday evening at a Bangkok hospital where she had been cared for since falling unconscious due to illness three years ago, according to the statement issued Friday.

"This loss is not merely bad news announced to the people, but an immeasurable grief in the hearts of the entire nation," Prime Minister Anutin Charnvirakul said in a televised speech. He said the princess was "a pride of Thailand," and that "her commitment to building a society of kindness, justice, and equality, will forever remain as a moral legacy for the nation, a guiding light for generations of Thais."

She will lie in state at the Grand Palace in Bangkok and her funeral will be held "with the highest honors according to royal tradition," the bureau's statement added, according to French news agency AFP.

The bureau said in May that her condition had deteriorated and medical devices and medications were supporting her lung and kidney functions, AFP reported.

A small group of mourners gathered in an atrium at King Chulalongkorn Memorial Hospital, where the princess had been treated. Most held framed or laminated photos of her throughout the years.

Pattamaporn Kaewkityakorn said she had arrived Thursday and spent the night there to show her support for the princess, unaware that the announcement of her passing would come the following morning.

"I know she was sick, but I wished there were a miracle," she said, her voice trembling. "I was saddened and shocked."

Bajrakitiyabha was active in justice reform efforts and best known for her Kamlangjai, or "Inspire" project to help rehabilitate incarcerated Thai women ahead of their release.

Bajrakitiyabha was hospitalized in December 2022 after falling unconscious while training dogs for an army exhibition. The palace said she had a mycoplasma infection, a bacterial infection usually associated with pneumonia.

Her father's New Year's greeting card for 2023 showed King Maha Vajiralongkorn and Queen Suthida garbed in somber black, which many Thais saw as confirmation of the gravity of her condition.

The princess was born on Dec. 7, 1978 to Vajiralongkorn, who was the crown prince at the time, and his then-wife, Princess Soamsawali. Vajiralongkorn has seven children by three of his four successive wives. Bajrakitiyabha was also known by the royal name Bajrakitiyabha Narendira Debyavati, used in formal state settings.

Prince Dipangkorn Rasmijoti, the youngest of the king's children, is the presumptive heir because sons take precedence in Thailand's line of succession. But Bajrakitiyabha's experience in public service raised speculation she was set to hold an important role in any future succession, perhaps as regent to a youthful monarch.

Bajrakitiyabha studied law at Thammasat University then went to Cornell University in New York state, where she earned a master's degree in law in 2002. She earned a doctorate at Cornell in 2005 with a dissertation concerning the protection of the rights of the accused. Scholarships to Cornell Law School and a program for the exchange of legal scholars between Thailand and Cornell were later established in her name.

After working briefly at the Thai Mission to the U.N. in New York City, she returned home and worked as a public prosecutor. She renewed her diplomatic career with an appointment as Thailand's ambassador to Austria from 2012 to 2014 before returning to her homeland to concentrate on criminal justice issues. In 2017, she was appointed a goodwill ambassador for the U.N. Office on Drugs and Crime.

In addition to working for the rehabilitation of female convicts, she was involved in other projects including a campaign to enhance the living conditions of women prisoners and promoting efforts to stem violence against women as an honorary U.N. goodwill ambassador for women. Her efforts led to the U.N. General Assembly adopting the "Bangkok Rules" on care and conditions for female prisoners.

"Society cannot grow if there is instability and injustice," Bajrakitiyabha said in a 2013 interview with The Associated Press.

"Without the rule of law, without a good justice system, it's always chaos," she said. "I think the rule of law is a very important pillar to development, to economic growth, and of course to human rights."

Bajrakitiyabha is survived by her parents and siblings.