Growing up in laid-back San Diego, Poomi Jensen was a world away from the pomp and circumstance of his Thai royal family. The grandson of the world's longest reigning monarchs, King Bhumibol Adulyadej of Thailand, the American-born prince spent much of his childhood not inside gilded palaces but on Southern California's sunny beaches.
The son of a Thai princess and an American businessman, Jensen attended schools in San Diego, family friends said. He went to live in Thailand with his mother a few years ago, after his parents waged a custody battle over him in a bitter divorce.
The 21-year-old prince was killed over the weekend by giant waves while jet-skiing at a Khao Lak beach resort in the Phang Nga province of southern Thailand, one of the regions hit hardest by the tsunami that killed at least 60,000 people in southern Asia.
Though the young man was autistic and attended special university classes while in Thailand, he often accompanied his mother, Princess Ubolratana, to official and social functions.
In a departure from Thai tradition, the princess was open about her son's disability, discussing his special needs in interviews and lending her name to fundraising drives for autism.
"Everyone knew [about his autism], and loved him and accepted him," said Chom Patchphradub, an executive producer for Network of Asian Telecommunications, TV and Radio in North Hollywood. "We loved him very much, the Thai people here. Everyone misses him."
His mother has accompanied his body back to Bangkok for royal funeral rites.
The body of the prince, known as Khun Poom to Thais, will lie in the palace for seven days in accordance with Buddhist tradition, after which it will be cremated in an ornate royal coffin, said Isinthorn Sornvai, the Thai consul general in Los Angeles.
In 1972, Jensen's mother scandalized her family and shocked international high-society circles when she fell in love with commoner Peter Jensen and relinquished her title so she could marry him. The princess, the eldest child of the king and Queen Sirikit, met Jensen while they were students at MIT.
Despite years of banishment from the royal household, the princess, known as Julie by her American friends, eventually reconciled with her parents.
The Jensens often picnicked and enjoyed the beach near their Del Mar home.
Peter Jensen, a locally prominent businessman, was involved in several high-profile ventures, including a gold-mining business in Northern California and companies in the water sales market.
The prince's father, who could not be reached for comment Tuesday, was said to be preparing to travel to Thailand.
"Peter is extremely devoted to his family, particularly to his children," said Michael P. George, a former business partner and chief executive of Western Water Co.
After raising Poomi Jensen and two daughters in suburban San Diego, the couple's fairy-tale romance crumbled.
When they divorced in 1998, Peter Jensen sought to keep his ex-wife from taking their son with her to Thailand. At a 1999 news conference in Bangkok, the princess accused her ex-husband of adultery and of "using the children as a bargaining chip" in their divorce.
According to San Diego Superior Court documents, Peter Jensen argued that his son's autism and sometimes violent behavior left the boy unable to function without supervision and that he might be endangered in Thailand.
But court officials who evaluated Poomi Jensen approved the move, concluding that "extensive resources" would be available to the boy in Thailand because of his protected position there. The older Jensen lost an appeal.
The prince's condition improved after he graduated from Torrey Pines High School in Del Mar, where he took special education classes, and moved to Thailand, where he had new doctors, his mother said in a January 2002 interview with the Bangkok Post. He was trying "to communicate with others and to socialize more," she said.
This year, palace officials announced that the prince would volunteer for military police service, even though his autism could have exempted him.
The cover of the May issue of Jewelry and Diamonds, a Thai high-society magazine, depicted the dark-haired royal in uniformed regalia. Inside, a glossy, 25-page photo spread showed him saluting and on horseback. The article also described him as so gifted with numbers that he could perform calculations involving distant calendar dates with speed and accuracy.
In addition to his parents, Poomi Jensen is survived by two sisters.