Spain's former king made his first trip home on Thursday after nearly two years in exile following a string of financial scandals, sparking widespread criticism.

Although prosecutors closed their probes into Juan Carlos I's affairs in March, revelations about the murky origins of his fortune have done irreparable damage to a figure once revered for his role in Spain's transition to democracy following decades of dictatorship.

"What we've heard in recent years has been very worrying for everyone regarding the institution of the head of state," Economy Minister and Deputy Prime Minister Nadia Calvino told Cadena Ser radio.

"There's no doubt we need some explanations."

The 84-year-old former monarch arrived on Thursday evening by private jet in Vigo in northwestern Spain ahead of a three-day regatta in the nearby resort of Sanxenxo.

His yacht, the "Bribon" -- Spanish for "rascal" -- is participating, and is the same vessel with which he and his crew won the world sailing title in 2017.

Juan Carlos smiled, waved and offered a thumbs up to onlookers as he arrived at the home of a friend in Sanxenxo where he will be staying.

On Monday, he travels to Madrid to visit his wife Sofia, his son King Felipe VI and other family members before leaving the same day for Abu Dhabi "where he has established his permanent residence", the palace said late Wednesday.

He has been living there since going into self-imposed exile in August 2020.

The visit reflects the former king's "desire to regularly visit his family and friends in Spain", it said, indicating such gatherings would be conducted "in a private setting".

- Government opposes palace sleepover -

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The 84-year-old former monarch arrived by private jet in Vigo in northwestern Spain ahead of a three-day regatta in the nearby resort of Sanxenxo. / © AFP

According to Spanish media, Prime Minister Pedro Sanchez's government strongly opposed any suggestion he be allowed to stay overnight at the royal residence, Zarzuela Palace.

The hard-line left-wing Podemos, Sanchez's junior coalition partner, expressed outrage over his visit.

"Anyone returning to our country with a record like that of king Juan Carlos I would be arrested as soon as they crossed the border and prosecuted," it tweeted.

After nearly 40 years on the throne, it was scandal that prompted Juan Carlos's fall from grace, forcing him first to abdicate in 2014 and then to flee to the United Arab Emirates, dogged by allegations of financial corruption.

In announcing his departure in 2020, the former monarch said he was leaving due to "the public repercussions that certain past events in my private life are generating", expressing hope Felipe could carry out his royal duties with the necessary "tranquillity and calm".

Some 18 months later, Spanish prosecutors shelved their investigations into his finances, concluding they did "not allow for any criminal action to be brought" against him.

They cited various reasons, including a "lack of incriminating evidence, the statute of limitations, the inviolability of the head of state and tax regularisation" payments he made in recent years.

Although they confirmed identifying "sums defrauded from the Treasury" between 2008 and 2012, they said the tax authorities had managed to recover more than five million euros, "an amount corresponding to the tax dues owed".

Since leaving, Juan Carlos has twice settled tax debts on undeclared income for over five million euros in what was widely seen as a bid to avoid being charged with a crime.

- Legally fine, ethically questionable -

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The former king is coming back to take part in a three-day regatta in which his yacht is participating / © AFP/File

"There is no longer any legal or judicial reason to stop the king emeritus from travelling to Spain but there are a wealth of ethical grounds that explain the commotion this has caused," an El Pais editorial said Thursday.

In a bid to try and restore the image of the monarchy, Felipe VI -- who took over as king in 2014 -- has sought to distance himself from his scandal-hit father.

In March 2020, Felipe ended his father's annual palace allowance, worth a reported 200,000 euros ($210,000), and renounced his own claim on what he would have inherited from the king emeritus.

Last month, he took steps with the government to increase the transparency of the monarchy with the publication of a decree requiring the palace publish its budget and make tenders public.

It also means the royal accounts will be audited, that senior palace officials must declare their personal wealth on taking up and leaving a post, and that gifts given to royals will be catalogued.