Spain's King Felipe VI has issued a decree stripping his sister Princess Cristina of her title as Duchess of Palma, the palace announced Thursday, as the royal sibling faces tax evasion charges in a scandal that has embarrassed the monarchy.

"The Official Journal of the state will tomorrow (Friday) publish a royal decree by which His Majesty the King will revoke the use of the title of Duchess of Palma de Mallorca by Her Royal Highness the Infanta Cristina," the palace said in a statement.

Cristina, 49, stands accused of taking part in tax evasion by her husband, the former Olympic handball player Inaki Urdangarin.

A judge ruled in December that she must stand trial on two counts of accessory to tax fraud, making her the first member of the Spanish royal family to be sent to the dock. No date has been set for her trial.

Both Cristina and Urdangarin have suffered a dramatic fall from grace since they married in 1997 in a lavish ceremony in Barcelona and were bestowed the titles of Duke and Duchess of Palma by Felipe's father, king Juan Carlos, who unexpectedly abdicated last year.

The couple's multi-million-euro mansion has been impounded by the courts and Cristina was notably absent from ceremonies marking Felipe's ascension to the throne in June 2014.

Urdangarin, 47, is accused along with a former business partner of creaming off six million euros ($6.6 million) in public funds from contracts awarded to Noos, a charitable foundation which he chaired.

Cristina's lawyers say she is innocent of any wrongdoing and that she trusted her husband to handle their financial affairs.

The corruption controversy has outraged Spaniards and helped sour the last years of the reign of Juan Carlos, who gave up the throne after nearly four decades hoping his son could freshen up the image of the monarchy.