According to Spanish newspaper El Pais, the King was shooting the breeze with a Honduran ambassador when the ringtone piped in:
But before accusing him of being creepy, give him a break and understand it's probably his GRANDCHILDREN. Juan Carlos never said what the ringtone actually was, but AOL news mentioned that he has a whole bunch of of the little runts, which would make sense. Moral of the story? The sensibilities of "royalty"—whatever that now means—are just as middlebrow as your own.