( AFP ) - The only sister of Thailand's revered King Bhumibol Adulyadej died of abdominal cancer on Wednesday at the age of 84, the royal household said.
Princess Galyani "passed away at 2:54 am (1954 GMT) on January 2, 2008," the household said in an announcement. The king's elder sister had been undergoing treatment at Bangkok's Siriraj Hospital since June last year.
Princess Galyani, an academic and lifelong student of French language and literature, was awarded the Grand Officer of the Legion of Honour, France's highest civilian distinction, in late December.
The king, who was close to his sister and visited her in hospital almost daily, declared a 100-day mourning period among royal family members and royal court officials.
Thai television stations interrupted their regular programming to announce the death of the princess and show footage of her life, with newscasters wearing black.
The princess began her career as a French professor at Bangkok's Chulalongkorn University, the kingdom's most prestigious academic institution.
After a 10-year break from teaching, she took over as head of the French department at Thammasat University in 1969 and later headed the Association of French Professors in Thailand, working to promote the French language.
Later in life, the princess devoted her energies to rural development and education, particularly in Thailand's impoverished northeast.
She also chaired several charities, including the Kidney Foundation, and helped secure funding for the construction of rural schools.
She married twice and had one daughter.
The 80-year-old king was taken to the same hospital in October last year after experiencing weakness on the right side of his body.
When he left hospital in early November, cheering crowds of well-wishers shouted "Long live the king."
On December 5, hundreds of thousands of people filled the streets around Bangkok's glittering Grand Palace to celebrate the king's 80th birthday.
King Bhumibol, the world's longest-reigning monarch, is treated with an almost religious devotion in Thailand and his health is a subject of great national concern.