Princess Cristina, the daughter of Spain's King Juan Carlos, has been subpoenaed by a Spanish court as a suspect in an investigation of alleged tax fraud and money laundering, the latest blow to the royal family's reputation.

Palma de Mallorca court judge Jose Castro ordered the 48-year-old princess to appear on March 8 for questioning about her partnership with her husband, Inaki Urdangarin, in a firm called Aizoon.

Mr Urdangarin is already under investigation for allegedly using his position to embezzle several million dollars in public contracts assigned to a supposedly non-profit foundation he set up.

The court cancelled a subpoena against the princess for questioning in that case last year.

The probes have seriously damaged the image of 76-year-old Juan Carlos, once one of Spain's most respected figures.

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