According to Thailand's royal palace says, the Thai King's eldest daughter, Princess Bajrakitiyabha, collapsed on Wednesday evening from a heart condition.
The oldest daughter of King Vajiralongkorn, and the most likely heir, collapsed northeast of Bangkok while she was training her dogs, according to the palace.
The 44-year-old was taken to a hospital nearby, and then flown by helicopter to Bangkok and is being treated.
Last night the palace said that she was “stable to a certain extent”.
There is no statement of her current health.
Kinwg Vajiralongkorn hasn't named Princess Bajrakitiyabha to the throne yet, but she is viewed by many as the most likely and suitable successor.
She is the most m accomplished of the royal circle, with post-graduate law degrees from two US universities.