In 2013, a law called the Succession to the Crown Act ended the centuries-old practice of a younger son superseding an elder daughter in the line of succession.

The line of succession has never moved beyond the vice president, though the country may have been closer to that scenario than anyone imagined.

Prince Charles, the Queen's oldest son, immediately ascends to the throne as King, putting his eldest son, Prince William, the Duke of Cambridge, first in line for the throne.

A government official is chosen as the designated survivor during high-profile political events to maintain the presidential line of succession in the event of a catastrophe. Here's how it works.