Watch a video clip of the conference row between President Chavez and King Juan Carlos

King Juan Carlos of Spain has led a charmed existence for much of the past three decades, enjoying the trappings of wealth, a deferential press and approval ratings that would be the envy of many other monarchs.

But 2007 is likely to go down as his annus horriblis.

The Royal Palace has had to confirm rumours that his eldest daughter, Princess Elena, is separating from her husband. The two married in Seville in 1995 amid great pomp and ceremony. The King was said to be deeply upset by the split.

The news capped what has been an unusually testing month for the King. On Saturday he lost his composure at a Spanish-Latin American summit in Chile, casting aside decorum and shouting “Why don’t you shut up!” at President Chávez of Venezuela.

Caught on television cameras, the phrase was an instant classic in Spain, where it plays as a ringtone on mobile phones throughout the country. Pop and dance versions of the royal rebuke began to appear within hours on internet sites such as YouTube.

The gesture was generally well received in Spain, where many people admired the King’s plain-speaking response to Mr Chávez’s repeated efforts to interrupt the Spanish Prime Minister. But some observers believe that the outburst has harmed Spain’s constitutional monarchy, restored only in 1975, as well as the image of the King.

It may, for example, undermine his efforts to forge a role for himself as a powerbroker in the Spanish-speaking world - a man above the political fray. For several months the King had been mediating in a row between Argentina and Uruguay over a paper mill on the river between the two nations. Despite his considerable diplomatic efforts, Uruguay opened the factory during the summit.

King Juan Carlos also came under attack in North Africa last week, after making his first visit for more than 30 years to two disputed Spanish enclaves on the African mainland. The trip to Ceuta and Melilla sparked an outcry by the Moroccan King, who gave warning that it would harm relations between the two nations. The two kings have long enjoyed a warm personal relationship; Spain depends on cooperation from Morocco on issues from illegal immigration to drug trafficking and Islamic terrorism.

Some observers believe that the controversies swirling around the Spanish monarchy could severely damage the institution. “The King has been in the limelight far too much of late,” said Tom Burns, a writer whose book on the Spanish monarchy is to be published this month. “And he’s been on the front pages for all the wrong reasons.”

Others, though, think some of the recent controversies could act in the King’s favour. “There are things in this catalogue [of events] that may have even benefited him,” said Paul Preston, the author of a biography of the King. The visit to Ceuta and Melilla, for example, had boosted his standing with the Right, he said, long the source of “mutterings” against the monarch.

Until this year, the King was virtually immune from public criticism, protected by a pliant press that refused to publish anything that might offend him. But the taboo is fast receding, even as the Government moves to punish those who offend the royal sensibilities.

On Tuesday two cartoonists from the weekly satirical magazine El Jueves were fined €3,000 (£2,140) for publishing a crude cartoon of Crown Prince Felipe having sex with his wife, Letizia. “Insulting the Crown” is a criminal offence in Spain, punishable by up to two years in prison.

Others have also fallen foul of the law, including nationalist protesters in the northeastern region of Catalonia. Eighteen Catalan youngsters could be prosecuted for burning pictures of the King during a protest this year.

The King was appointed by the Spanish dictator Francisco Franco to succeed him after his death in 1975.

But instead of continuing his regime, the King earned the respect of many Spaniards by steering the country towards democracy. He is also credited with quashing an attempted coup by a section of the military in 1981, an event that caused his standing among Spaniards to soar.

The Venezuelan President sparked worries yesterday that the spat could grow into a full-scale diplomatic crisis. Mr Chávez said that he would “profoundly revise” Venezuela’s economic and political ties with Spain, and threatened reprisals against Spanish companies in the country.

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