Firstborn Daughters Can Now Ascend British Throne Rule change agreed to today By Evann Gastaldo, Newser Staff Posted Oct 28, 2011 8:55 AM CDT 21 comments Comments Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge attend a fundraising Gala at St James's Palace on October 13, 2011 in London, England. (Getty Images) (Newser) – Thanks to a rule change agreed to today, Prince William’s firstborn can ascend the throne, even if that firstborn happens to be a girl. The change to the royal succession rules was approved by leaders of the 16 countries for whom the British monarch is head of state; they also decided to scrap the rule prohibiting a monarch or heir from marrying a Catholic. The change to the centuries-old rules will take effect beginning with children of William and Kate, the Los Angeles Times reports. Said Prime Minister David Cameron, "The idea that a younger son should become monarch instead of an elder daughter simply because he’s a man, or that a future monarch can marry someone of any faith except a Catholic—this way of thinking is at odds with the modern countries that we’ve all become."