Spanish King Juan Carlos' son-in-law will be questioned Saturday by a judge investigating a corruption case as press reports make new revelations that cast a growing shadow on the entire royal family.
Inaki Urdangarin and former partner Diego Torres are suspected of syphoning off millions of euros paid by regional governments to the Noos Institute, a charitable organisation which Urdangarin chaired from 2004 to 2006.
The money was meant to cover the cost of staging sporting and tourism events.
Both men have denied any wrongdoing and have not been charged with any crime.
Spain's two main daily newspapers, El Pais and El Mundo, on Monday published e-mails supposedly sent by Urdangarin which appear to indicate that the king backed and closely followed his business career closely.
The revelations are embarassing for the royal palace which has tried to mark a clear border between Urdangarin's business affairs and the royal family, especially Urdangarin's wife, Princess Cristina, since the scandal erupted at the end of 2011.
Princess Cristina was a non-executive director at the Noos Institute but has not been called to appear in court for questioning.
In one of the e-mails allegedly sent by Urdangarin in March 2005 published Monday, he wrote to Corinna Wittgenstein, a twice-divorced German aristocrat described by Spanish media as a close friend of the king, to ask for her help in landing him a job at an international sports organisation.
"Excuse my silence during these last few days. I wanted to check with my father-in-law and Alberto Aza as well before I give you feedback," he allegedly wrote in the e-mail in a reference to the king and the former head of the royal household.
During a court appearance on Saturday, Torres told the judge leading the investigation that "the royal palace supervised the activities of the Noos Institute", El Pais reported Sunday.
Torres also "directly called into question the king" by revealing that the monarch was referred to as "the boss" in internal discussions at the Noos Institute, the newspaper reported.
Torres' defence team have turned over nearly 200 e-mails, including those published in Spanish media on Monday, to the investigating judge.
The royal family sidelined Urdangarin, who acquired the title of Duke of Palma in 1997 when he wed Cristina, from all official royal activities at the end of 2011 and last month he was removed from the family website.
The 45-year-old former Olympic handball player was jeered in February last year when he appeared in court to be questioned for the first time as part of the probe.
He will be grilled again at the court in Palma on Saturday, the same day that Carlos Garcia Revenga, secretary to the king's daughters Elena and Cristina is set to be questioned in the case.
Revenga will be questioned about his role at the Noos Institute and "his possible work as an advisor" to Urdangarin, the court source said.
The palace has said it would keep Garcia in his post and would take no action until he goes before the judge.
Earlier this month the court said it would begin freezing assets belonging to Urdangarin and his former business partner after they missed a deadline to pay bail of 8.2 million euros ($11.1 million).
Since the bail was applied in a civil case the two will not go to jail for not paying the sum.