Once news of Charles's unprecedented letter became public there was an immediate response from the apparently peeved Sussexes, with a spokesman for the couple briefing: 'We were a little surprised not to have been told about this in advance.'

But royal author Robert Jobson told the Daily Mail that he is convinced this apparent gripe from the Sussexes will be met by stony silence from Buckingham Palace.

Mr Jobson said: 'It has only been a couple of weeks since the Duke and Duchess returned to Britain but already there were reports of Meghan planning to do charity work and Harry taking on military commitments - as pseudo royals. It seemed a kind of mission creep.

'In the light of this it was felt that it was important for the King to clarify that nothing has changed with regard to the Duke and Duchess and that - at their own elective choice - they became and remain private individuals and not working royals.