The King was reportedly told to "back off" after attempting to check on the wellbeing of Sir Ranulph Fiennes, the 82-year-old explorer who has not been seen publicly for more than two years.
Sir Ranulph's wife and legal guardian, Louise Millington-Cotes, is said to have rejected the enquiry from Buckingham Palace, angered that her phone number had been passed on without her permission. The monarch was concerned about his friend's health and isolation, according to reports.
Explorer's achievements and current situation
Sir Ranulph, who climbed Mount Everest, became the first person to visit both the North Pole and South Pole by surface means, and was the first to completely cross Antarctica on foot. He has Parkinson's Disease and is reported to have been given a false name by Ms Millington-Cotes as he has been moved between care homes.
Charles is believed to have thought Sir Ranulph would be "thrilled" to know the King cared about him, but the explorer's second wife allegedly threatened to contact a solicitor and the police.
Contact attempts and reaction
The King's equerry allegedly contacted an individual who had written a letter asking how the monarch could reach Sir Ranulph and was given a phone number for Ms Millington-Cotes, The Telegraph reported. She claimed the contact had caused her husband, whom she married in 2005, "immense distress".
Anton Bowring, who took part in the Transglobe Expedition with Sir Ranulph between 1979 and 1982, is thought to have previously written to Charles' private secretary to say the explorer was "in a very poor state".
Friends' concerns and police involvement
Mr Bowring was later contacted by the King's then equerry, who said Charles was "most concerned" and wanted to help. But Mr Bowring allegedly received a text from Ms Millington-Cotes reading: "I'm going to be changing my phone number because of you!!!"
Ms Millington-Cotes is 23 years Sir Ranulph's junior, and they married a little over a year after the death of his first wife. Friends such as TV presenters Ben Fogle and Bear Grylls have sought clarity over Sir Ranulph's location, and Mr Fogle has asked police to investigate how the explorer is being kept "isolated".
