Whenever The Queen travels, either as part of her official royal duties or simply for a holiday, the logistics of transporting the Monarch around the world are a little more complicated than just hopping in a cab to the airport and jumping on a plane, like the rest of us do.
There are strict rules and protocol that must be followed in case of an emergency and every possible scenario must be thought of, including the unlikely event that the Queen becomes ill or injured while travelling.
And now royal expert Adam Helliker has revealed the rather unusual item the Queen's staff always have on handy when she travels - a large supply of her own blood.
"The Queen always travels with a supply of blood which is placed in the responsibility of whichever doctor is on duty and accompanies her on duties and royal tours," Mr Helliker told The Sun.
"This means that in a country where speedy access to a reliable blood supply cannot be guaranteed, such as remote parts of Africa, the sovereign and her consort will be able to receive blood transfusions if they were required for a medical emergency."
The blood is taken care of by her personal assistant, plus the Queen always travels with three doctors in case she falls ill.
They research nearby hospitals that are appropriate for Her Majesty well in advance of the trip, in case she ever needs to be admitted.
Mr Helliker explained the Queen's extensive blood supply "is regularly topped up from her own blood" to avoid "any infection from someone else's blood."
"She will have kept the supply topped up with regular deposits on the months before a trip abroad," he added.
"So it's just like someone making voluntary blood donations - the difference being that she will be the only recipient if it's ever needed - that 'blue blood' will never find its way to an ordinary patient."
It's also well known that all members of the royal family travel with a black outfit, in case someone close to them dies while they are away.
In 1952, the Queen was on a royal trip in Kenya when she was informed of the death of her father King George IV.
WATCH BELOW: See Queen Elizabeth's day on a plate. Story continues after video.
While on her way back to London, her staff discovered she only had a floral dress with her and no appropriate black mourning outfit to face the world's press.
So her plane was grounded in London and stayed on the tarmac until a staff member could deliver a black dress on board, which she promptly changed into before leaving the plane and facing photographers.
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