A baby girl born to Prince William and his wife Catherine would make history by automatically becoming queen one day under plans to end centuries of royal gender inequality.
Moves are underway in Britain and across the Commonwealth to dump ancient laws putting royal sons ahead of their sisters in the line of succession to the throne.
Currently, a monarch's first-born son becomes heir to the throne even if he has an older sister.
But under the proposed changes, a first-born girl would automatically become heir ahead of any younger brothers.
If the Duke and Duchess of Cambridge's first-born child is a girl, she will be third in line to the throne behind her grandfather, Prince Charles, and father Prince William.
Prince William's younger brother, Harry, will move from third to fourth in line.
Leaders at the Commonwealth Heads of Government Meeting (CHOGM) in Perth in October 2011 unanimously agreed in principle to change Britain's succession laws, which date back more than 300 years.
New Zealand has been co-ordinating how the changes will be implemented by the 16 Commonwealth realms.
New Zealand and Britain are the only countries within the group of 16 realms to include succession laws in their domestic legislation.
The changes deal with what is known as male preference primogeniture, which gives sons precedence over daughters in the line of succession.
Proposals also included moves to end the ban on royals succeeding to the throne if they marry a Catholic.
However, while leaders at CHOGM agreed in principle to the changes, formal approval is still needed from the parliaments of the 16 Commonwealth realms where the Queen is head of state.
The British government is expected to give its consent shortly, with the revamped laws to apply to any royal births from the date of the CHOGM leaders' decision.