It's no secret that the Royal Family enjoys giving each other nicknames.
But on top of their private monikers, they also have top-secret code names allotted to them for security purposes.
These code names can represent people and events. Last year, plans for the Queen's death were given various names depending on her location at the time - including Operation London Bridge.
King Charles has also collected his fair share of code names over the years, including a rather unexpected one that was given to him by the Secret Service when he travelled to the US in 1971.
The code name in question is 'Unicorn'.
As previously reported by The Express, this code name was given to him during a royal visit to America, but it's not known why this specific word was chosen.
However, it's likely some sort of reference to the UK as the unicorn is one of the nation's symbols and is also the national animal of Scotland.
At the time of the visit, Charles would also have been the Prince of Wales, and a white unicorn features on the coat of arms of the Prince of Wales.
But 'Unicorn' isn't the only code name associated with the King.
Ahead of his coronation on May 6, the ceremony has had its own special code name and has been known as Operation Golden Orb to all those involved.
This is a reference to the Sovereign's Orb, one of the crown jewels, that the monarch will carry during the coronation ceremony.
And much like his mother before him, Charles also has a code name for his death - which came to light in 1988 when he disappeared during a ski trip after an avalanche and his family was told to prepare for the worst.
Operation Menai Bridge was the code name used to describe his possible death back then. The name was taken from the Welsh suspension bridge and also reflected his role as the Prince of Wales.
However, as he is now King, this code name might have been updated or passed on to Prince William, who is the current Prince of Wales.
