It looks like the ex-King of Spain, Juan Carlos I, has been dodging the taxman. This is the latest in a large number of scandals affecting the Spanish royal family.
According to the links below, he used a "friend" - Corinna zu Sayn-Wittgenstein - domiciled in Monaco to hide property beneficially owned by himself.
The "friend" appears to be implicated in a whole network of dodgy financial dealings, including the "Nóos Scandal" involving the ex-king's son-in-law Urdangarín and others.
More here (in Spanish) and here (in English).