The spat between Spain's king and Venezuela's president took a new turn as Hugo Chavez asked if the monarch had advance knowledge of a 2002 coup.
On Saturday King Juan Carlos told Mr Chavez to "shut up" at a summit in Chile after the president said ex-Spain PM Jose Maria Aznar was a "fascist".
The king was widely applauded in the media back home.
On Sunday Mr Chavez said the king was "imprudent" and asked if he knew in advance of the brief coup against him.
As he left the Ibero-American Summit in Chile's capital, Santiago, Mr Chavez questioned whether Spain's ambassador had appeared with Venezuelan interim president Pedro Carmona during the two-day coup in 2002 with the monarch's blessing.
"Mr King, did you know about the coup d'etat against Venezuela, against the democratic, legitimate government of Venezuela in 2002?" he asked at a news conference.
"It's very hard to imagine the Spanish ambassador would have been at the presidential palace supporting the coup plotters without authorisation from his majesty."
Spain's El Mundo newspaper quoted Mr Chavez as saying that on Saturday the king had "got very mad, like a bull".
"But I'm a great bullfighter - ole!" he said.
On Sunday, Mr Chavez said he hoped the spat would not damage relations.
"But I think it's imprudent for a king to shout at a president to shut up. Mr King, we are not going to shut up."
The spat began after Mr Chavez called Mr Aznar, a close ally of US President George W Bush, a fascist, adding "fascists are not human. A snake is more human."
King Juan Carlos (r) won plaudits back home
Current Spanish PM Jose Luis Rodriguez Zapatero then said: "[Former Prime Minister] Aznar was democratically elected by the Spanish people and was a legitimate representative of the Spanish people."
Mr Chavez repeatedly tried to interrupt, despite his microphone being turned off.
The king then leaned forward and said: "Why don't you shut up?"
According to reports, the king used a familiar term normally used only for close acquaintances - or children.
The king then stormed out as Nicaraguan President Daniel Ortega stepped in to back Mr Chavez.
In Spain, the king's actions were applauded.
El Mundo said: "The king has put Chavez in his place in the name of all Spaniards."
It said the rebuke was "something that should have been said [to Mr Chavez] a long time ago".
The left-leaning El Pais said Mr Chavez's outburst was "intolerable".
The BBC's Steve Kingstone in Madrid says the king has experienced a turbulent few months, including a visit to two disputed Spanish enclaves in north Africa and being the subject of anti-monarchist protests that saw his photograph burned.
However, our correspondent says it seems this row may have done the monarch a power of good as he approaches his 70th birthday.