The secret codeword for when the Queen dies has been leaked and we're already in tears.

As the longest-reigning living monarch, Queen Elizabeth II has seen a lot of changes during her 55 year reign.

While most people can’t imagine a time where she isn’t around, there’s a special group of people who have long been preparing for her death.

But before you get alarmed, it’s not some undercover plot. It’s actually their job..

An article published in The Guardian yesterday broke the news of Operation London Bridge, the top secret plan that will be implemented in the days after the Queen passes away.

The article leaks the (now previously) secret codeword that will be used to inform the first few people of her death - and we're already in tears.

The phrase? "London Bridge is Down".

Listen: The Crown, Netflix's drama of Queen Elizabeth's early days is a must-watch. Post continues after audio.

The first person to say it will be Sir Christopher Geidt, the Queen's private secretary who will contact the Prime Minister and say the codeword on secure lines.

The news will then be sent from the Foreign Office's Global Response Centre to the 15 governments outside of the United Kingdom (including Australia) where the Queen is also the head of state as well as 36 other nations of the Commonwealth.

The last time a British monarch died was George VI 65 years ago. The code word used to spread the message was "Hyde Park Corner" to prevent switchboard operators from finding out.

Even in the digital age, it is hoped that the news will be controlled or kept secret for some time before it is made public.

Using secure communication lines detectable only by special equipment, governors general, ambassadors and prime ministers will be the first to be informed.

The formal announcement will go out as a newsflash to the Press Association and international media simultaneously.

At the same time, a black-edged notice will be pinned to the Buckingham Palace gates by a footman in mourning clothes, while the palace website will be changed to a single page displaying the same text on a dark background.

It's an event some news organisations have been preparing for for years.

According to the Guardian article, the deputy editor of the paper has a list of prepared stories pinned to the wall and The Times is said to have 11 days of coverage ready to go.

Sky News and ITN have been rehearsing the death of the Queen for years, substituting the name "Mrs Robinson" and royal experts have already signed exclusive contracts to provide commentary for the channels.

The BBC news team were reportedly hauled to work on quiet Sunday mornings for 30 years to perform mock storylines about the Queen Mother's death prior to her actual passing in 2002.

Nearly everyone is in agreeance that her passing, funeral and subsequent mourning will be a monumental event.

However, it's safe to say they'll probably need to come up with a new codeword.