He made the announcement in a letter directed towards his son, King Felipe VI.

The 82-year-old said he was willing to help prosecutors with the investigation and was available for interviews.

Juan Carlos took over from General Franco, after the latter's death in 1975 and helped Spain achieve democracy from dictatorship.

He abdicated the throne in 2014 in favour of son Felipe, after a corruption investigation involving his son-in-law was started.

"Guided by the conviction to best serve the people of Spain, its institutions, and you as king, I inform you of my decision at this time to leave Spain. A decision I make with deep emotion but with great serenity," the letter read.

Meanwhile, King Felipe VI has started to distance himself from his father, ever since the Apex Court said it aims to investigate the former king and his role in a high-speed rail contract in Saudi Arabia.

According to reports, Spanish firms won the €6.7bn contract to work on the Mecca-Medina rail project.

Not just his own country, Switzerland has also opened an investigation against him as it involves Swiss banks.