A Spanish court has summoned King Juan Carlos's youngest daughter Cristina over suspected tax and money-laundering crimes.
The Infanta Cristina, 48, has been linked to the business affairs of her husband, former Olympic handball player Inaki Urdangarin, who is under investigation for alleged embezzlement of public funds.
The decision by a court in Majorca is a major blow to the prestige of the 76-year-old Spanish king.
Battling scandal and ill health, King Juan Carlos appeared tired as he presided over a military parade while on crutches yesterday in his first public appearance since undergoing an operation to replace his left hip in November.
Majorcan judge Jose Castro has been investigating the corruption allegations against the Infanta Cristina's husband since 2010.
In summoning the Infanta Cristina, he overruled opposition by the public prosecutor.
In a written ruling, the judge said he had decided to hear the Infanta Cristina's testimony "about alleged tax and money laundering crimes", summoning her to appear in March as part of an investigation that could lead to formal charges.
A palace spokesman said he wanted to express his "respect for judicial decisions" and declined further comment.
Manos Limpias, a right-wing pressure group, lodged the suit against the Infanta Cristina alleging tax evasion and money laundering, although tax authorities have not brought any charges and public prosecutors have said there is no case to answer.
The judge in the Majorca court is investigating allegations that Mr Urdangarin and a former business partner embezzled €6 million in public funds via the Noos Institute, a charitable foundation that he chaired.
The Infanta Cristina was a member of the board of Noos and with her husband jointly owned another company, Aizoon, which investigators suspect served as a front for laundering the embezzled funds.
The Majorca judge had summoned her on suspicion of corruption once before, in spring 2013, but that decision was overruled following an appeal by the prosecutor.