Exiled Spanish king hiding in Abu Dhabi following corruption scandal, newspaper claims
Other media have singled out Portugal or the Dominican Republic as possible destinations for the former monarch who abdicated in 2014, but his exact location has yet to be pinned down.
The royal palace has refused to reveal where Juan Carlos is living, saying he will announce it himself if necessary.
Pro-monarchy newspaper ABC wrote that the 82-year-old boarded a private jet on Monday from Vigo in northeastern Spain along with one aide and four bodyguards.
Seven hours later, the plane landed at a business airport in the capital of the United Arab Emirates.
A photo of a man alleged to be Juan Carlos in a face mask disembarking from a plain was published by Spain's NIUS media group on Saturday.
According to a flight plan ABC said it had seen, the jet was registered as departing from Paris to avoid arousing suspicion.
In fact, it took off from Paris on Sunday before making a stop in Vigo to pick up Juan Carlos.
The paper says he is now well shielded from paparazzi photographers after travelling by helicopter from the airport to the luxurious Emirates Palace hotel, where he is reportedly staying in the $12,000-a-night presidential suite.
It added that high temperatures have so far kept him indoors.
However a manager at the hotel denied the former king was there.
Mysterious €100 million gift from Saudi king
Juan Carlos has long had warm relations with the Gulf monarchies, and Spanish press reports say a transfer of $100 million to one of his Swiss bank accounts from late Saudi king Abdullah has come into investigators' sights.
After abdicating over corruption allegations stemming from public statements by a former mistress, Juan Carlos announced on Monday that he was quitting Spain so as not to undermine his son King Felipe VI.
The former king used the Swiss account until it was closed in 2012, when he transferred the remaining money in it - nearly $65 million - to his mistress, German businesswoman Corinna Larsen, according to Swiss newspaper La Tribune.
Larsen told Swiss investigators he had transferred to her nearly 65 million euros in the Bahamas, "not to get rid of the money", but "out of gratitude and out of love", according to Spanish daily El Pais.
La Tribune said a Geneva prosecutor in 2018 opened a criminal investigation into "suspected money laundering" regarding these transactions and formally accused Larsen, Mirabaud bank, a lawyer and a businessman - but not Juan Carlos.
Swiss prosecutors have declined to comment on the case.
Meanwhile, Spanish prosecutors in 2018 opened a probe into the Saudi high-speed rail contract, which was awarded to a consortium of Spanish companies. The 450-kilometre (280-mile) link between Mecca and Medina was inaugurated in 2018.
Spain's Supreme Court in June announced an investigation to determine whether the contract had involved the "crime of corruption in international transactions" and whether Juan Carlos was legally responsible - but only for acts committed after his abdication in 2014, because of the immunity he enjoyed until then.
Corruption is one of the most difficult crimes to prove, according to sources at Spain's public prosecutors office.
And it will be hard to argue that the 100 million dollars Juan Carlos allegedly received from Saudi Arabia was a kickback for the high-speed rail contract, which was awarded three years later.
Investigators looking into the former king's bank accounts could search for evidence of money laundering and tax fraud, according to the sources.
But money can be considered to have been laundered only if its source is illegal, the sources said.
So even if it is proven that Juan Carlos received millions of euros from Gulf royals, from Kuwait to Oman to Saudi Arabia as press reports allege, it would still have to be shown that this was not a perfectly legal gift.
And if they found that it was not a mere gift, prosecutors would still have to prove that the former king used this money - by investing it or transferring it from one bank account to another - after he lost his immunity when he abdicated in 2014.
If the former king moved his money abroad without declaring it, he can be held liable for tax fraud, but only for events going back five years. Anything before that falls under the statute of limitations.
But while there is no formal investigation, Socialist Prime Minister Pedro Sanchez said in June "the entire Spanish population are receiving disturbing information which is troubling for us all, including me".
Agencies contributed to this report.
Follow us on Facebook, Twitter and Instagram to stay connected