The royal suspect: Spain's Princess Cristina linked to corruption scandal

Spain's Royal Family lurched towards a new low point in what could be their most serious credibility crisis in decades when King Juan Carlos' daughter, Princess Cristina, was named as a suspect in a multimillion euro fraud and money-laundering case involving her husband, Iñaki Urdangarin.

For the first time since modern Spanish democracy began in the mid-1970s, an inside member of the country's monarchy, once blessed with a squeaky-clean reputation, will now have to respond to a court summons in Palma de Mallorca on 27 April.

As yet nobody has been charged in the case. But it has been gripping Spain for the past two years, thanks to a seemingly interminable spiral of allegations concerning Mr Urdangarin and the siphoning off of millions of euros of public money from regional government contracts to the supposedly non-profit making organisation, Nóos, he co-directed from 2004 to 2006.

Since 2011, a welter of gory financial details from the case – alleged tax dodges of more than half a million euros via an NGO for children with terminal illnesses, apparent charges of €700,000 for a 13-page financial report for a football club stadium and the liberal use of offshore companies in Belize and the UK – has been leaking steadily from Spain's judicial system on to the front pages.

The royal family have been trying to distance themselves from Mr Urdangarin, a former Olympic handball player who received the title of the Duke of Palma when he married Princess Cristina in 1997. More than a year ago, in December 2011, Mr Urdangarin was suspended from all official royal engagements. A royal spokesman then described his behaviour as "less than exemplary", his profile was removed from the royal website and his figure in Madrid's waxwork museum was shifted from the royalty tableau.

In two appearances in court in Palma de Mallorca, Mr Urdangarin has both proclaimed his innocence and insisted that his wife had no knowledge of his activities, despite her being a Nóos board member.

According to the Spanish media, emails have now emerged that appear to indicate that Princess Cristina had some degree of knowledge of her husband's financial affairs. Earlier this week a second attempt by Mr Urdangarin to have the emails, produced by his former business partner, Diego Torres, thrown out of court as invalid evidence was again rejected.

That was hardly good news for Mr Urdangarin. Nor was a demand, made last month, by presiding magistrate José Castro that he post a joint bond of €8.1m. And now, in a dramatic U-turn, after previously rejecting several calls for Princess Cristina to be declared a suspect, Mr Castro, has now decided that she should be.

According to El País, the 19-page court statement explaining his decision also says that "there is no evident indication that the Princess participated in the daily running of Nóos". But the statement also warned "the law is the same for everyone" – the same words used by the king in a 2011 Christmas address that was widely taken as a reference to his son-in-law.

When questioned about the latest development on Wednesday, a Spanish royal spokesman said that they do not comment on judicial decisions. Both of Spain's major parties, the PP and PSOE, have also avoided issuing statements.

The emails in question form part of dozens released by Mr Torres since April last year in what is widely seen as an attempt to avoid possible punishment by turning the spotlight on the royal involvement in Nóos.

Within hours of the news breaking, Spanish media had reported that the country's anti-corruption authorities would appeal against Princess Cristina's summons.

Fraud inquiry: The key names

Iñaki Urdangarin

The former Olympic handball player married Princess Cristina in 1997. He retired in 2000 and began running the not-for-profit Nóos Institute, organising sport-related events.

Princess Cristina

The youngest daughter of Juan Carlos is seventh in line to the throne. She runs social welfare programmes at a Barcelona-based charitable foundation.

Diego Torres

The former business school lecturer was Urdangarin’s partner in the Noos institute until the investigation intensified. He has released dozens of emails taken from Noos business archives concerning Urdangarin. He denies any wrongdoing.