King Juan Carlos I due for heart surgery tomorrow

The 81-year-old Rex Emeritus – who abdicated in favour of his son, the now King Felipe VI, in June 2014 – had one of his regular complete health checks on June 11 and 12, the result of which was that he needed cardiac surgery.

As it was not programmed until late August and given that the Royal family uses private medical care and does not have to concern itself with waiting lists, it is believed the need for an operation was not hugely urgent.

King Juan Carlos I officially retired from public duties on June 2 this year, but has still taken part in several private engagements.

The next of these is likely to be at tennis star Rafa Nadal's wedding to his childhood sweetheart Meri Perelló in October, since the former monarch is a great friend of the world number two player.

He has been under knife numerous times in the last decade, although each occasion has been for mobility-related issues rather than illnesses, including a knee replacement in 2011 which was carried out again in April 2018.

Otherwise, his only non-joint-related surgical intervention was in April this year for an early stage case of skin cancer which was cut out 'as a precaution', did not need further treatment and is said to have been fully cured as a result.

King Juan Carlos I is pictured here earlier this year with his granddaughter, Victoria Federica de Borbón y Marichalar.