By Chayut Setboonsarng
BANGKOK (Reuters) - She is a Thai princess who became a champion sailor, married a foreign commoner, earned two degrees in the United States, starred in a soap opera and tragically lost her son in the 2004 Indian Ocean tsunami.
Thailand's Princess Ubolratana Rajakanya Sirivadhana Barnavadi on Friday set her sights on a new role: prime minister of the Southeast Asian kingdom as candidate for a party loyal to ousted ex-premier Thaksin Shinawatra, arch-rival to the pro-military and ardently royalist establishment.
But her bid to enter politics - and thereby break a long-standing tradition of the royalty - looked likely to be cut short just hours after it had begun.
Her brother, King Maha Vajiralongkorn, late on Friday moved to block her candidacy, saying her involvement in politics was "inappropriate" and unconstitutional.
Ubolratana said in an Instagram post earlier it was her right as a citizen to accept the nomination which could see her becoming prime minister after a March 24 general election.
She has disregarded royal tradition before - most notably by marrying an American fellow student, Peter Jensen, while studying at the Massachusetts Institute of Technology (MIT) when she was 21 years old.
The princess was required to give up the titles Her Royal Highness and Chao Fa (Lady of the Sky), which were bestowed on her birth in 1951 in Switzerland, where her father, King Bhumibol Adulyadej, was attending university.
After her marriage and 1973 graduation from MIT, she moved with her family to California and used the name Julie Jensen, earning a master's degree in public health at the University of California, Los Angeles.
She had three children - daughter Ploypailin Jensen, son Bhumi Jensen and younger daughter Sirikitiya Mai Jensen.
She lived in the United States for years, though frequently visited her parents, the much-revered King Bhumibol, who died in 2016, and Queen Sirikit.
Ubolratana grew up close to her father and during her teens shared his love of sports, becoming his favourite partner in tennis, badminton and small-boat sailing. The pair shared a gold medal in sailing at Southeast Asian games in 1967.
Her trips back to Thailand became more frequent in the 1990s, when she began joining the queen at charity events and balls.
She appeared on the covers of Thai magazines, at society parties and fashion events and founded a charity for children orphaned by HIV-related illnesses.
Ubolratana and Jensen divorced in 1998, and she brought their three children back to Thailand to resume her royal duties.
The children received Thai citizenship and were treated as royals. She was increasingly included in royal ceremonies and used the royal title "Tunkramom Ying", meaning "Daughter to the Queen Regent".
But perhaps because she had relinquished her formal royal titles, Ubolratana appeared less bound by the formalities of the court.
She launched an anti-drug foundation for at-risk youth and teens, for which she occasionally sings and dances at awareness-raising programmes.
Ubolratana also starred as a historical princess in a 2003 Thai soap opera set in the Ayutthaya period of the 14th to 18th centuries, and in an action movie in which she played a tough journalist facing danger as she works to uncover a dastardly plot.
But her new life in Thailand was marred by tragedy in 2004 by the Indian Ocean tsunami that killed more than 200,000 people in Asia. When the tsunami struck, Ubolratana was on holiday with two of her children at a southern beach resort.
They fled the giant waves but her 21-year-old son Bhumi was swept away and died.
Ubolratana mourned and threw herself into charity work.
Her entry into politics has come as a shock to many, but in recent years there had been signs of closeness to exiled ex-prime minister Thaksin, who was deposed in a 2006 coup and whose sister, Yingluck Shinawatra, served as an elected prime minister until the latest coup in 2014.
Ubolratana and Thaksin's daughter exchanged public messages of support on social media after her father, King Bhumibol, died in 2016 and her brother assumed the throne.
In 2018, images of Ubolratana, Thaksin and Yingluck watching a World Cup soccer match together in Russia appeared on social media.
More recently, Ubolratana appeared to be signalling a closeness to ordinary folk on her Instagram account, with posts in past weeks showing her enjoying street food and complaining about a spell of heavy pollution in Bangkok.
(Editing by John Chalmers, Robert Birsel and Peter Graff)