As her heir, the Prince of Wales will be the first to know of his mother's passing. He will probably be at her deathbed, unless she dies suddenly or unexpectedly.
On his mother's death, Charles will be king immediately. His siblings and children will kiss his hands. Then constitutional government will kick in.
The Prime Minister will need to be informed immediately of the passing of the head of state.
For a time, her subjects will not know she is dead and that the throne has passed to her eldest son. Governors general, ambassadors and prime ministers will learn first. But in the world of 24-hour news it will not stay secret for long.
This increased responsibility means Charles is much more than a deputy, stepping up to stand in for the Queen. As we approach the end of 2018, a more accurate description of his role is ‘Shadow King’, as it is he, not Her Majesty, who is now doing most of the ‘heavy lifting’ for the monarchy at home and abroad.
His increased workload sees the Prince regularly working 14-hour days and he carries out more than 600 engagements a year at home and abroad.
Indeed, now that she does not travel overseas, Charles's royal tours representing her across the globe are state visits.
There are those who insist the Queen is still as sprightly, fit and sharp as she was two decades ago. This is not true. She is still sharp on matters of state, but requires her schedule to reflect her age and capacity. Even she thinks those loyal subjects who believe nothing needs to change are deluding themselves.