It is the second time Inaki Urdangarin, the Duke of Palma, has been questioned about millions of euros given by regional governments to a charity he ran, the BBC reported Saturday.
The 45-year-old Urdangarin and his former business partner, Diego Torres, are suspected of siphoning off into offshore accounts and companies controlled by the duke the funds given to the Noos Institute to organize sporting events.
The duke has denied any wrongdoing, but the scandal has further eroded the Spanish public's support for the royal family, the BBC said.
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