AS THE nation enters its mourning period for Queen Elizabeth II, the country is preparing for significant changes under a new monarch. 

As King Charles III is formally declared as King in a historic Accession Council ceremony, the British public is marking an end of an era with imminent changes from stamps to passports ahead.

Her death brings an end to a 70-year reign, the longest in history, having ascended the throne following the death of her father, King George VI on 6 February 1952.

The beloved monarch's portrait adorns coins, notes and stamps and that is before we consider her initials which embellish uniforms and postboxes across the country.

King Charles: The life and times of our new monarch

The British public has already begun asking what Queen Elizabeth's official initials ER will change to following Her Majesty's passing.

What does the ERII initials mean and what does Regina mean?

You may be familiar with the Queen's ERII Royal Cypher which has adorned everything from royal documents to post boxes.

ER or ERII stands for Elizabeth Regina which means Queen in Latin.

The Roman Numerals II refers to Her Majesty being the second Queen named Elizabeth.

The term initially caused controversy in Scotland since Elizabeth I did not rule over Scotland.

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What will ER change to now that King Charles III is declared King? 

In fact, the objections at the start of the Queen's reign were so strong that a Post Office pillar box in Edinburgh which included the ERII cypher was defaced and later blown up.

Now that King Charles III has officially been declared King, the new monarch is expected to use CIIIR monogram.

This stands for Charles III Rex with Rex being the Latin word for King.

In criminal court cases, the R to denote the Crown will now stand for Rex rather than Regina (the Queen).