A brief statement by the Royal Household Bureau said the 78-year-old queen, the wife of Thailand’s constitutional monarch, was discharged from Bangkok’s Chulalongkorn Hospital after doctors determined her treatment had been successful.

“The doctors said the (queen’s) general condition and her heart rate had become normal after the treatment,” it said. “No rapid heartbeat was detected again.”

The queen entered the hospital on Thursday evening. An earlier statement was vague about the treatment she received.

King Bhumibol Adulyadej, 82, has been staying in Bangkok’s Siriraj Hospital since being admitted on Sept. 19, 2009 for what the palace described at the time as an inflammation of the lungs. The reason for his extended stay has not been explained.

Sunday’s statement said “the queen has left Chulalongkorn Hospital to stay at Siriraj Hospital like before,” implying that she had been staying previously with the king at Siriraj Hospital, though it was the first official mention of it.

Official statements about the royal family are traditionally formal and discreet.

Bhumibol, the world’s longest-serving monarch, has been king of Thailand for 64 years. He has no formal political role, but he is regarded as the sole unifying figure in a politically polarized country.

The king’s health is an extremely sensitive topic in Thailand because of concerns that the succession may not go smoothly. The heir apparent, Crown Prince Vajiralongkorn, does not yet have the stature or moral authority of his father.

Open discussion of the matter — and all matters pertaining to the royal family — is limited by strict laws that make criticism of the monarchy punishable by up to 15 years in prison.