His Royal Highness Crown Prince Maha Vajiralongkorn presided over rites commemorating the 63rd anniversary of Coronation Day of His Majesty the King, who had to suspend his own appearance due to illness.
Her Majesty the Queen, who has been hospitalised since July, also did not attend the ceremony, which took place on Sunday morning at the Amarin Winitchai Throne Hall.
The event was attended by Her Royal Highness Princess Maha Chakri Sirindhorn and the crown prince's consort, Her Royal Highness Princess Srirasmi.
According to the 65th announcement of the Royal Household Bureau released on Sunday, a team of royal physicians has advised His Majesty the King, 85, to suspend all royal activities for a while.
The announcement said the result of an x-ray reveals that the inflammation in the lungs of His Majesty, found on April 28, has reduced. His Majesty is able to sleep but cannot yet take much food and is still tired.
Previously, the bureau said Their Majesties the King and Queen would appear at the ceremony.