The trip by Vacharaesorn Vivacharawongse, 42, comes at a fraught time for the Thai royal family, with the monarch’s eldest daughter in a coma since December.
Vacharaesorn, who works at a law firm in New York, visited the Foundation for Slum Child Care, which is supported by the royal family, and greeted well-wishers.
Clad in jeans and a casual black shirt, he posed for photographs in front of portraits of his father and his grandfather, King Bhumibol Adulyadej, who died in 2016 after a 70-year reign.
“I am delighted to return … I have been away for a long time, 27 years,” Vacharaesorn told reporters at the Bangkok foundation.
“It is like a dream come true to be back,” he said.
The Royal Palace has not commented on the visit. The Palace Household Bureau did not respond to requests for comment.
Many Thais have been surprised by Vacharaesorn’s return. A picture of him in a “tuk-tuk” auto-rickshaw in Bangkok, that he posted on Monday on his Facebook page, which has more than 80,000 followers, received tens of thousands of likes.
On X, the social media platform formerly known as Twitter, the hashtag #SonOfTenReturnToThailand was mentioned almost 390,000 times. His father’s formal title is King Rama X.
Those who saw Vacharaesorn were impressed.
“I am very moved, he has been away for a long time. To me he is still a member of the royal family,” said Angsana Seeprasit, 66.
Vacharaesorn is the second of four sons of King Vajiralongkorn’s second wife, Sujarinee Vivacharawongse, a former actress whom the then-crown prince divorced in 1996.
He has no formal royal title though he technically retains a status bestowed when he was a child as a grandson of a monarch.
He, his mother, three brothers and one sister were estranged after the 1996 divorce, in which his mother was publicly accused of adultery, and they moved abroad.
Vacharaesorn’s younger sister was later re-embraced by the royal family and given the royal title Princess Sirivannavari Nariratana. She is a fashion designer and equestrian who competed in the 2014 Asian Games for Thailand.
The thrice-divorced King Vajiralongkorn has seven children. He is married to Queen Suthida, his former chief bodyguard whom he wed days before his coronation in 2019.
The 71-year-old monarch has not named an official heir.
In late December, the king’s eldest child, Princess Bajrakitiyabha Narendira Debyavati, 44, collapsed due to a severe heart condition. She remains in a coma.