MADRID (AP) — Spain's former monarch, Juan Carlos I, has been admitted to hospital for a heart operation.

The 81-year-old king emeritus will undergo the operation Saturday in Madrid's Quiron clinic.

There were no further details on the operation but Spanish media cited palace officials as saying it was programed following a checkup in June, indicating it was not an urgent procedure.

Arriving at the clinic late Friday, he told reporters, "You'll see me on the way out."

Juan Carlos retired from public life in May. He abdicated in 2014 in favor of his son, ending a near 39-year reign.

Revered by many Spaniards, Juan Carlos was considered a key figure in Spain's transition from dictatorship to democracy following the 1975 death of Gen. Francisco Franco.