Juan Carlos lost his constitutional immunity after his abdication in 2014 and can therefore be prosecuted for any wrongdoings committed after that date. The alleged donations were between 2016 and 2018.

He will have committed a financial crime if he failed to declare more than €278,000, or a fiscal crime if he failed to declare more than €275,000, El Päis reports.

Investigators are also trying to establish whether Mexican businessman Allen Sanginés-Krause donated the money to the former king or merely made it available for him to spend.