Charles, who on Friday marked the first full day of his reign following the death of his mother, Queen Elizabeth II, has spent a lifetime waiting to take on the top job.
Here are some key numbers associated with the new monarch.
The number of times Charles contracted coronavirus. He spent a week isolating after first testing positive in March 2020. In February this year he tested positive again but showed no symptoms.
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Age at which Charles became first in line to the throne after his grandfather, King George VI, died in 1952 and his mother became Queen Elizabeth II.
Age at which he acquired the impeccable side parting that became his personal style signifier.
Number of years Charles spent with Diana Spencer after a fairytale wedding in 1981. They separated in 1992, with Diana blaming the breakdown of the marriage on his affair with Camilla Parker Bowles. They divorced in 1996.
Number of letters dubbed the "black spider memos" sent in Charles' spidery script to Tony Blair's government in 2004-2005. In the missives, Charles urges government action on issues ranging from inadequate army equipment to the plight of the Patagonian Toothfish.
The number of years Charles has owned his venerable Aston Martin DB6 convertible, which he converted in 2008 to run on bioethanol made from wine and cheese.
His elder son, Prince William, used the car to leave Buckingham Palace with his new wife after their wedding in 2011.
The number of years a clothing company in Worcester, central England, had to wait to be repaid the £453.15 ($527 in today's money) in debt run up by King Charles II in the 17th century for army uniforms.
The prince who became Charles III on Thursday paid the money back in 2008, minus the interest.
The number of tonnes of CO2 emissions generated by Charles and Camilla in the year ending March 31, 2019, the most recent year for which they provide records.
The king, an environmentalist, has been criticised for his liberal use of private jets.
The number of people who have benefitted to date from the Prince's Trust, which Charles set up in 1976 with his Royal Navy severance pay to help youngsters from disadvantaged areas.
It is also the amount of the donation towards his charity that Charles reportedly accepted from the family of 9/11 mastermind Osama bin Laden in 2013.
The number of followers Charles and Camilla have on Instagram. By comparison, Prince William and Kate, the Duke and Duchess of Cornwall and Cambridge, have 13.9 million.