The body of the Thai king’s eldest daughter was brought to the royal palace in Bangkok on Saturday, as thousands of black-clad mourners lined the procession route.
Princess Bajrakitiyabha, known as Princess Bha, died aged 47 on Thursday following an abdominal infection.
She had already spent more than three years in a coma due to a cardiac condition.
Thousands of mostly older mourners sat in sweltering temperatures along the 10-kilometre route to the Grand Palace from Chulalongkorn Hospital, where the princess had been treated.
Her body arrived at the palace at around 5:00pm local time in a solemn and orderly procession.
Police closed roads and traffic ground to a halt in parts of Bangkok’s commercial centre as the royal motorcade passed, led by King Maha Vajiralongkorn and Queen Suthida.
It is the second bereavement for the royal family in months, after Queen Sirikit, the king’s mother, died in October at the age of 93.
Bajrakitiyabha was the only child of Vajiralongkorn’s marriage to Princess Soamsawali.
The 73-year-old king, who has seven children from four marriages, has not announced his chosen heir, although succession rules favour men.
Strict rules govern what can and cannot be said about the Thai royal family, who are protected from criticism by lese-majeste laws that carry prison sentences of up to 15 years per charge.