She has visited 116 countries on 265 official visits during her 63-year reign, making her the most travelled monarch in history.
Instead her eldest son will pick up the slack, taking on an increasing prominent role as Britain's global ambassador.
Foreign Office officials are said to have been impressed by Charles's assured performance on the international stage, particularly in the Middle East.
One mandarin described the prince as "providing not just the continuity, but the continuity that matters".
One aide said: "The Prince of Wales is picking up more of HM's duties than ever, particularly as regards foreign trips, and this will continue to increase.
"It is something he believes is his duty but, more importantly, he feels he can make a real difference doing. He will be going anywhere the Government requires."
Charles already carries out more than 600 engagements each year, a work ethic inherited from his mother who at 89 undertook almost 400 last year.
The Queen will overtake great-great-grandmother Queen Victoria's record of 23,226 days, 16 hours and 23 minutes on the throne at 5.30pm on Wednesday.
- Daily Mail
