Succession laws to the British throne are about to be changed after 300 years, meaning Prince William and pregnant Kate Middleton's first child will one day be monarch regardless of gender.
The Succession to the Crown Bill was steered through the House of Lords on Monday and will soon land on the Queen's desk for final approval.
Previous laws discriminated against females in the British Monarchy, favouring men in the direct line of succession.
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Deputy Prime Minister Nick Clegg, who has been a vocal supporter of the bill since it was introduced at the Commonwealth Heads of Government meeting in October 2011, described the change as a "historic moment".
"I am proud the British Parliament has taken this step to end centuries of religious and gender discrimination," he said.
In December last year, the government and other Commonwealth countries agreed to press ahead with the bill ending bias against female royals.
That decision came in the same month William and Kate announced their baby news.
At the time, Nick Clegg said it was by "wonderful coincidence" that formal consents from other Commonwealth realms were received just as the royal couple revealed they were expecting their first child.
"The government will soon introduce the Succession to the Crown Bill, which will make our old-fashioned rules fit for the 21st century," Mr Clegg said.
"It will write down in law what we agreed back in 2011 – that if the Duke and Duchess Cambridge have a baby girl, she can one day be our Queen even if she later has younger brothers."
The sex of a royal heir has always been kept secret and the world will now have to wait until a formal announcement is made when the baby is born in July.