A one euro coin has turned up in Spain bearing the face of cartoon couch potato Homer Simpson instead of that of the country's king, a sweetshop owner told Reuters on Friday.

Jose Martinez was counting the cash in his till in the city of Aviles, northern Spain, when he came across the coin where Homer's bald head, big eyes and big nose had replaced the serious features of King Juan Carlos.

"The coin must have been done by a professional, the work is impressive," he told Reuters.

The comical carver had not taken his tools to the other side of the coin displaying the map of Europe. So far, no other coins of the hapless, beer-swilling oaf have been found in circulation.

"I've been offered 20 euros for it," said Martinez.