Although Prince William is not the current heir apparent, the birth of his third child has got royal fans wondering what will happen when he eventually becomes King.
Queen Elizabeth II is the current reigning monarch, being the longest-serving British monarch in history, and her eldest son, Prince Charles, is the first in line to the throne upon her death.
Prince William, who is Charles’ eldest son, is the second in line to the throne and is guaranteed to become King one day.
So will Kate be known as Queen when her husband sits on the throne?
Currently Kate, who married William on 29 April 2011, is formally known as Catherine, Duchess Of Cambridge.
While she is still more commonly known as Kate Middleton – or Duchess Kate – when Prince William, the Duke Of Cambridge, ascends the throne following King Charles III – or should that be King George VII’s – death, her title will change.
There's much talk over what Camilla, Duchess Of Cornwall's name will be when Charles ascends the throne.
On their wedding day, Clarence House revealed that when Charles becomes King, presuming he will not abdicate, Camilla will become known as Princess Consort.
Traditionally, as dictated by English common law, the wife of the ruling monarch is called Queen Consort: Kate Middleton will be known as when William ascends the throne.
A Queen Consort shares her husband's social rank and status, although not his military or political powers.
There is no historical or legal reason why Camilla would be known as Princess Consort and this year, Clarence House removed the statement dictating this, suggesting she will, after all, be known as Queen Consort.
A Queen Consort can take the title of Queen, so Camilla would become known as Queen Camilla.