Thailand's Princess Bajrakitiyabha Narendira Debyavati, the oldest child of King Maha Vajiralongkorn, has been taken to hospital after suffering heart problems.
A statement from the Royal Palace confirmed Princess Bajrakitiyabha, 44, lost consciousness on Wednesday at Pak Chong in the north-eastern province of Nakhon Ratchasima while training her dogs.
She was taken to the local hospital before being flown by helicopter with a royal medical team to Bangkok once her condition had "stabilised to a certain extent".
The palace statement said the princess was receiving treatment at King Chulalongkorn Memorial Hospital in the Thai capital.
Princess Bajrakitiyabha was in Pak Chong for her dogs to compete in the army's Working Dog Championship.
She is one of King Vajiralongkorn's three children who have formal titles, making her eligible for the throne under a 1924 Palace Law of Succession.
King Vajiralongkorn has not yet named an heir to the throne.
Princess Bajrakitiyabha was born in Bangkok's Dusit Palace on December 7, 1978 to then Crown Prince Vajiralongkorn and his first wife Princess Soamsawali Kitiyakara.
She celebrated her 44th birthday last week.
After studying law at Bangkok's Thammasat University, she went on to complete her post-graduate law studies in New York at Cornell University.
She has spent most of her career with the Office of the Attorney-General in Thailand and has worked extensively on guidelines and programs to help female prisoners.
She has also been a UN Women National Ambassador and was Thailand's Ambassador to Austria from 2012-2014.
Last year, she was appointed Chief of Staff of the Royal Security Command with the rank of General.
