The Spanish king's son-in-law has been jeered by hundreds of protesters as he arrived at a court to answer questions about suspected fraudulent deals.
Inaki Urdangarin, the Duke of Palma, was questioned on Saturday about whether he used his high-profile status to secure lucrative deals for a nonprofit foundation he ran, then fraudulently diverted some of the money for personal gain. He has not been charged with a crime.
The investigation into the alleged financial misdeeds has embarrassed the monarchy in a country hard hit by a financial crisis and high unemployment.
As news of the investigation began to fill Spanish newspapers last year, King Juan Carlos announced in December that his son-in-law would no longer take part in official ceremonies with the rest of the family.
Urdangarin, who lives in the United States, is a former professional and Olympic handball player who acquired his title by marrying the king's daughter, Cristina, Duchess of Palma.
On Saturday the duke arrived at the court accompanied by his lawyer, Mario Pascual Vives, then braved a 25m walk in front of hundreds of jeering protesters, some carrying banners reading, "Juan Carlos, if you knew, why did you keep quiet?"
A handful of pro-monarchy supporters were also present.
The somber-looking Urdangarin stopped before some 350 journalists from around the world that had gathered outside the court to give a brief statement.
"I appear to demonstrate my innocence, my honour and my professional activity," he said, adding he is convinced his statements to the court would "clear up the truth".
The duke is suspected of securing large contracts from regional governments for his foundation, then subcontracting the work to private companies he also oversaw, sometimes charging the public unrealistically inflated prices and syphoning some of the income to offshore tax havens.
The duke's alleged misdeeds took place in between 2004 and 2006. Urdangarin, the princess and their four children moved to Washington in 2009 as the investigation began to heat up.
The case exploded in the media late last year as Spain was buffeted by Europe's debt crisis, its economic growth grinding to a halt and already huge jobless numbers swelling.
Under Spanish law, the court will decide whether the prosecution has adequate evidence to file charges against the duke.