Because of a throat infection Thai King Bhumibol Adulyadej failed to make his traditional birthday eve address on Thursday. It will be his 81st natal day on Friday.

Instead Crown Prince Varjiralongkorn announced over Thai radio his father's medical condition. The king is on medication and physicians placed him on a saline drip.

Some political observers opined the king chose to be silent after Thailand went through another political crisis with the takeover by citizens over the airport, which prompted a Thai court to oust the prime minister from his post and ban his political party from participating in future elections for several years.

Thitinan Pongsudhirak, political scientist at Chulalongkorn University, told the International Herald Tribune, "It would have been a very difficult speech in a deeply polarized time... It is possible that His Majesty did not want to be used by one side or another, did not want to be seen as tipping the balance to one side or another."

The aging monarch, held in high esteem and well-loved by Thais, previously had two heart surgeries, a spinal operations and an apparent stroke. It is the first time in his over six decades of rule that King Bhumibol did not make his birthday eve speech.