The 44-year-old princess collapsed on December 14, while she was training her dog for a competition in the city of Nakhon Ratchasima, northeast of Bangkok.
She is being cared for in hospital, where her heart, lungs and kidneys are kept functioning artificially. She is also receiving antibiotics.
The doctors have diagnosed that she suffered from a mycoplasma bacterium which caused “a heart inflammation” and “severe cardiac arrhythmia”, according to the court’s statement.
Bajrakitiyabha is the only child from the marriage of King Maha Vajiralongkorn (regent name Rama X) to his cousin, Princess Soamsawali. Since her father’s accession to the throne in 2016, she has had a prominent role in public affairs and has been talked about as a possible crown princess.