The Peoples' Queen

In 1981, Queen Elizabeth dies unexpectedly after not sleeping for days.

This causes her newly wed son, Prince Charles to become the new king, and his young wife, Diana to become Queen at only 20

Now they have to deal with marriage, the UK and a very (reasonably) depressed Prince Phillip

Also, in this story, Diana and Charles have a 2-3 year age gap instead of a 12-13 year age gap