After nearly 66 years on the throne, Queen Elizabeth II is the longest reigning monarch in British history and has been a constant and calming force amidst the fast-paced changes their country has faced, making it even more inconceivable to think about what happens when she dies. Since Buckingham Palace doesn't shy away from procedure, it's no surprise there's already a comprehensive plan in place for what happens after she passes, known as Operation London Bridge. On the day Queen Elizabeth II dies, her death will elicit a comprehensive plan that has been in place since the 1960s. What will happen when Her Majesty's reign comes to an end and how will Britain mourn the loss? Here is what we know so far.

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