A Spanish judge has charged King Juan Carlos's youngest daughter with tax fraud and money laundering.

Judge Jose Castro said in a 200-page ruling following a lengthy probe that there was enough evidence Princess Cristina had committed crimes, summoning her to court on March 8.

The infanta's husband Inaki Urdangarin has already been charged with fraud, tax evasion, falsifying documents and embezzlement of €6 million (£5m) in public funds through his charitable foundation.

Both deny wrongdoing.

The case is one of many high-level corruption scandals that have undermined faith in public institutions at a time of severe economic crisis marked by deep spending cuts.

Opinion of the royal family in particular has sunk to its lowest-ever level. A January 5 poll showed more than 62 per cent want the once-popular king to abdicate.

His standing has been damaged by the corruption scandal and by huge public outrage over a luxury African elephant-hunting safari he took in 2012 in the midst of the country's financial crisis and swingeing austerity cutbacks.

While they have been under investigation, the princess and her husband have ducked public appearances.

She and her four children moved to Geneva last year where she works for a Spanish bank.

Judge Castro has been investigating corruption allegations against Princess Cristina's husband since 2010.