The Duchess of Cambridge is pregnant with her third child. And the birth of the third baby will see Prince Harry become sixth in line to the throne, even though Princess Charlotte remains fourth in line to succeed.
According to the current order of succession, Prince Charles is followed by Prince William and Prince George followed by Charlotte and Harry.
The Succession to the Crown Act of 2013 before the birth of George means that boys born into royal family no longer get preference over their sisters in the line of succession.
This means that Charlotte will remain as fourth in line to the throne - regardless of whether the new royal baby, due next Spring, is a boy or a girl.
The Royal Succession bill was rushed through Parliament during Kate’s first pregnancy to ensure that William and Kate's first child could succeed to the throne, regardless if the baby was a boy or a girl.
It was in accordance with the 2011 Perth Agreement and also ended the disqualification of a person who married a Roman Catholic from the line of succession, and removed the need for those outside the first six persons in line to the throne to seek the monarch's approval to marry.
The Queen approved the historic change by giving royal assent to the Succession to the Crown Act in April 2013, before the birth of George in July.
Under the ancient rules of male primogeniture, first born royal daughters in direct line to the throne were overtaken by younger male siblings.
This would therefore be the first time the Act would come into play....