Demonstrators in 24 cities around Spain gathered on Sunday to call for the prosecution of former King Juan Carlos who left the country in a cloud of controversy in August.
Protesters wielded red, purple and yellow Republican flags as they rallied for Carlos to be held culpable for the corruption in his financial history, from money laundering to tax evasion.
The 82-year-old former monarch relinquished the throne in 2014 and has been living in the United Arab Emirates since leaving Spain in order to avoid causing further embarrassment for his son, King Felipe VI.
"We are here to call for the corrupt former king to be prosecuted and to demand a republic," Juan Morillo, 74, a retired teacher, told Reuters at the protest.
Carlos is not formally under investigation but could become the target in inquiries in Spain and Switzerland for alleged corruption associated with a €6.8 billion (£6.1) high-speed Saudi train contract won by Spanish firms.
Spain’s Supreme Court prosecutor is considering whether to extend the corruption investigation into the train contract, which would formally involve Carlos.
The former king has not commented publicly on the allegations, while his lawyer Javier Sanchez has said he is at the disposition of prosecutors if necessary.
In the wake of royal scandals, a poll published last Monday by the left-wing Platform for Independent Media found 90.9 per cent of Spaniards preferred establishing a republic in the country.
Meanwhile, 34.9 per cent said they supported the royal family and 24.2 per cent said they did not know.
In August, a poll published by the pro-monarchy ABC newspaper found 33.5 per cent favoured a republic while 6 per cent did not know and 4.1 per cent were indifferent.
Earlier this month, thousands of demonstrators in Barcelona protested a visit from King Felipe and prime minister Pedro Sánchez amid continued tensions between the restive region and national authorities.
Small groups of protesters gathered to burn photos of the King. Members of this Catalonia separatist movement, supported by roughly half of the region's 7.5 million inhabitants, want to create a republic in the northeast corner of Spain.
The demonstrations had come less than two weeks after Catalonia’s regional chief, Quim Torra, was removed from office by Spain’s Supreme Court which had ruled him unfit to hold office after Torra violated election laws.
A cloud of allegations has shrouded Juan Carlos over the last few years, all with severe consequences for the stability of the fragile monarchy and the former monarchs popularity for restoring democracy after the death of General Franco in 1975.
King Felipe stripped his father of his annual stipend in March while renouncing his personal inheritance after reports emerged that Carlos was in line to receive millions of euros from a secret offshore fund with ties to Saudi Arabia.