The "King Emiret" could not be convicted due to the statute of limitations, prosecutors said.
Spanish prosecutors have shelved two investigations into Juan Carlos I over alleged financial wrongdoing.
The former king moved from Spain to Abu Dhabi in 2020 over judicial investigations into his business dealings and taxes.
But prosecutors in the Spanish Supreme Court said on Wednesday that they didn’t find evidence that could be prosecuted as any possible fraud fell out of the statute of limitations. The monarch had also been protected by immunity until his abdication eight years ago.
The decision now paves the way for the "King Emerit" to return from the United Arab Emirates -- a highly divisive issue in Spanish society.
Juan Carlos says he will remain based in Abu Dhabi "for the time being" but will return for periodic visits, according to royal officials.
The former king wrote a letter to his son over the weekend -- King Felipe VI -- expressing his desire “to visit family and friends”.
Investigations into the former king did recover €5.1 million in fines and taxes for income that Juan Carlos had failed to declare, prosecutors said.
One of the probes involved offshore accounts in Jersey that couldn’t currently be linked to the 84-year-old.
The second investigation centred around an alleged €65 million commission for mediation on a high-speed railway contract between the Saudi Arabian cities of Medina and Mecca.
Prosecutors said they couldn’t find a link between the “gift” given to Juan Carlos and the project, which was executed by a Spanish consortium.
A Swiss probe on money laundering involving some of the funds was also dropped last year, although Geneva prosecutors fined a Swiss bank for failing to alert authorities about Juan Carlos’ transactions.
In a statement, the former king’s lawyer said that prosecutors had cleared the former king of "any illicit conduct susceptible to criminal reproach".
Some Spanish citizens say the former king's alleged fraud should be overlooked, given that he had helped steer the country from dictatorship to democracy in the late 1970s and early 1980s.
But a growing number have demanded more accountability for members of the royal family, following the investigations.
Juan Carlos abdicated in favour of his son Felipe in 2014 following a series of scandals within Spain's royal family.
“I am aware of the importance to public opinion of past events in my private life," Juan Carlos wrote in the letter.
"I sincerely regret [it], as I also feel legitimate pride in my contribution to democratic coexistence and freedom in Spain, the result of the collective effort and sacrifice of all Spanish people,” he added.
Since becoming king, Felipe has tried to distance himself from his father, removing the former monarch from the royal house’s payroll to help rebuild the Spanish crown’s image.