Will and Kate’s Royal Baby Girl Could Be Queen if Rules of Succession Change

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ABC News’ Suzan Clarke and John Berman report:

A centuries-old tradition that gives preference of succession to the British throne to princes rather than princesses could soon come to an end.

The British parliament has proposed changing the rules – in place for more than 300 years – to allow females to become monarch. Currently,  females can only do so if they have no brothers, which is why Queen Elizabeth II was allowed to become ruler.

British Prime Minister David Cameron is taking the first steps to change to change the rules so that the first child of Prince William and Kate Middleton could benefit.

“I am very clear that it is an issue that we ought to get sorted, and I would be delighted to play a part in that,” Cameron said of his efforts.

There’s no indication that Middleton is pregnant.

The prime minister wants to update the Act of Settlement, the 310-year-old agreement that not only gives women second-class status, but would also lift a centuries-old ban on British monarchs marrying Roman Catholics.

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In a letter to Commonwealth nations that recognize the queen as their head of state, Cameron described the ban as a “historical anomaly” because it does not bar those who take spouses of other faiths.

“We do not think it can continue to be justified,” he wrote.

The 16 Commonwealth nations that recognize Queen Elizabeth as head of state  – countries that include Australia, Canada, Jamaica and Tuvalu - must give their formal approval before the proposal can take effect.

“It’s really complicated,” Dickie Arbiter, a former spokesman for Buckingham Palace, told ABC News.

The United Kingdom is a parliamentary democracy with a constitutional monarch. The monarch serves as the head of state, while the prime minister serves as the head of government.

The Associated Press contributed to this report.