What happens when Queen Elizabeth II passes away has been planned out for years, in an operation with the codename London Bridge.

The Royal Family announced her death on Thursday afternoon, Sept. 8.

The plans that follow go into immense detail, including how Britain’s prime minister was notified, a 10-day schedule from her death to the funeral and plans for London to be flooded with mourners to pay their respects.

It's important to note that plans could change in reality, and any final decisions are up to the new King Charles III and the Royal Family.

According to POLITICO, which obtained a copy of the London Bridge planning last year, the day of the queen’s death will be internally known as “D-Day,” and her funeral will be held on D-Day+10.

On the day of her death, the queen’s private secretary would have first informed the prime minister, who would in turn notify the cabinet secretary and the most senior British officials.The public was notified by the royal household.

According to The Guardian, the phrase “London Bridge is down,” would be said on secure phone lines.

On social media, the United Kingdom’s government accounts and its website will display a black banner. Flags will be lowered to half-staff across British government buildings.

POLITICO reported that plans will be set in motion for the new King Charles to speak that evening to the nation, before he begins his ascension to the throne the next day. The plans call for a 6 p.m. address, but her death was announced after that time on Thursday, so it's unclear when the address will take place.

There will be a proclamation confirming Charles as the new monarch, read both at St. James’ Palace and the Royal Exchange in the City of London.

All other government business will be suspended for ten days.

During that time, the Queen’s coffin will return to Buckingham Palace before a procession that takes it to Westminster Hall, The Guardian reported. 

King Charles will go on a tour of the United Kingdom, receiving messages of condolence from Scotland to Northern Ireland.

Then, the Queen’s coffin will lie at Westminster for public viewing 23 hours per day for four days, then closed off to public view until her funeral, which will take place 10 days after her death.

According to POLITICO, transportation officials are concerned “that the number of people who may want to travel to London could cause major problems for the transport network, and lead to overcrowding in the capital.”

That includes the possibility that the capital becomes “full” for the first time “as potentially hundreds of thousands of people try to make their way there — with accommodation, roads, public transport, food, policing, healthcare and basic services stretched to breaking point.”

The funeral will be a National Day of Mourning and will be held at Westminster Abbey, according to The Guardian.

They report that at 11 a.m., when the coffin reaches the Abbey doors, the country will go completely quiet — public transportation, television, everything will stop.

The archbishop will speak inside, and the royal family will say their prayers.

The Royal Navy will then transport her coffin in a grand procession of 23 miles — surrounded by thousands of mourners from all over the U.K. and the world — to Windsor Castle, where Britain’s royal leaders are buried.