Thailand ? A pall of uncertainty hung over normally joyous celebrations of the Thai king’s birthday Friday after the revered monarch failed to appear for ceremonies because of an illness that has shocked a nation reeling from political turmoil.

The ailing, 81-year-old King Bhumibol Adulyadej was scheduled to take part in a birthday ceremony at the Grand Palace, but it was canceled because of an illness that also prevented him from delivering his annual birthday speech Thursday, local media said.

The much-revered constitutional monarch has been a cornerstone of stability, stepping in to defuse political crises and halt bloodshed during his six decades on the throne.