If the Duchess of Cambridge gives birth to a girl first, her daughter can become Queen. The 300-year-old rule has been scrapped, giving equal rights to both boys and girls in succession to the throne.

Queen Elizabeth, opening the Commonwealth Heads of Government Meeting in Perth, Australia, praised the power of women to change the world. The reform now means that if the Duke and Duchess of Cambridge's first child is a girl, she will lead over any younger brother in the order of succession.

The 16 Commonwealth "realms" that have the British monarch as their chief of state, which include Canada and Australia, agreed to scrap outdated laws which also ban anyone in line of succession from marrying a Roman Catholic.

British Prime Minister David Cameron announced the changes at the meeting. Politicians were unanimous in agreeing in the reform of the royal succession.

"The theme this year is 'Women as Agents of Change'. It reminds us of the potential in our societies that is yet to be fully unlocked and it encourages us to find ways to allow all girls and women to play their full part. We must continue to strive in our own countries and across the Commonwealth together to promote that theme in a lasting way beyond this year," the Queen said at the opening.

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