King Juan Carlos's youngest daughter, the blonde-haired, 48-year-old Cristina, was summoned this week to appear on th at a court in Palma de Mallorca as a suspect in alleged tax and money-laundering crimes.
Cristina is suspected of being tied to the activities of her husband, Inaki Urdangarin, a 45-year-old former Olympic handball player who has been under investigation since 2011 over the suspected embezzlement of money from public bodies.
"I am absolutely convinced of the princess's innocence," one of her lawyers, Jesus Maria Silva, told reporters in Barcelona.
"The princess's innocence comes obviously from her faith in the marriage and the love for her husband," said Silva, of the law firm Roca Junyent, which is handling her defence.
"When one person is in love with another, she trusts, has trusted and will carry on trusting that person come hell or high water. Love, marriage and mistrust are absolutely incompatible," he said.
The princess and her husband are equal owners of Aizoon, a company suspected by the investigating judge, Jose Castro, of being a front for the diversion of embezzled funds.
The judge had summoned Cristina on suspicion of corruption linked to her husband's activities once before, in spring 2013, but that decision was overruled following an appeal by the prosecutor.
Castro then opened a new line of inquiry, scrutinising her tax declarations and bank accounts for incriminating travel, restaurant or family party expenses before deciding to summon the princess as a suspect.
Cristina's lawyers have vowed to appeal the latest summons. If allowed to stand, it will mark an ignominious and historic first for a direct relative of the Spanish king.
Whether or not the court summons leads to formal charges, it represents a grave new blow to the prestige of the princess and to the institution of the Spanish monarchy.
Already, the image of the royals has suffered during the investigation into Urdangarin and his former partner Diego Torres.
They are suspected of syphoning off money paid by regional governments to stage sports and tourism events to the non-profit Noos Institute, which Urdangarin chaired from 2004 to 2006.
Both men have denied any wrongdoing and neither they nor Cristina have been formally charged with any crime.
Cristina, who works as the director of social welfare programmes at Barcelona-based financial services group La Caixa's charitable foundation, took a posting in Geneva last year.