ThinkSpain said the royal couple declined to hold an official celebration of their golden wedding anniversary, but the palace has produced a CD album to mark the occasion called "Their Majesties' Golden Wedding: 50 years, 50 pictures."
The king and queen were married May 14, 1962, in Athens, Greece, in a Catholic and Orthodox service witnessed by 137 kings, queens, princes and princesses from all over Europe, ThinkSpain said.
The news outlet did not say exactly how the couple spent their half-century anniversary Monday.
Members of Congress to keep receiving porn magazine
Disney's 'Jessie' to feature network's first engagement