The birth of the Duke and Duchess of Cambridge’s third child, Prince Louis, marked an important part in royal history and how succession to the throne works.

Princess Charlotte is the first princess not to be superseded by the later birth of another brother. Born 2 May 2015, Charlotte is fourth in line to the throne (after the Prince of Wales, then her father William and her oldest brother, George).

Styled Her Royal Highness Princess Charlotte of Cambridge, a title and style given to all Prince William’s children under the letters parent issued by Queen Elizabeth in 2012, the princess benefits from the Perth Agreement, which replaced male-preference primogeniture with absolute primogeniture, i.e. oldest first.

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At the moment, Prince Louis is fifth in line to the throne, followed by the recently-married Prince Harry. Then, Prince Andrew and his children, followed by Prince Edward and his son and daughter (his daughter is the oldest), with Princess Anne as thirteenth in line.

However, what isn’t as well known is that if Princess Charlotte has children they wouldn’t automatically inherit the titles HRH or Prince or Princess because royal titles come through the male line. That’s how the law stands presently, though that too may change.

Queen Elizabeth offered Peter and Zara Phillips, the children of Princess Anne, a royal title when they were born though their parents declined the offer.

Princes and princesses with royal styles and titles, such as the children of Prince William, don’t usually bother with surnames. If one is required, though, the male line descendants of Queen Elizabeth and Prince Philip, can use Mountbatten-Windsor.

The name ‘Charlotte’ has a long tradition in European royal circles. One of the current princess’s ancestors was a Princess of Wales. Princess Charlotte Augusta of Wales (1796-1817) was the only child of King George IV (born while he was still Prince of Wales) and Caroline of Brunswick.

The couple had a famously frosty marriage—the Prince Regent later stated they’d only had sex three times, which explains their single child status—and separated within weeks of marriage. Caroline gave birth to Charlotte nine months after their wedding. The birth didn’t reconcile the couple.

If she’d outlived her grandfather (George III) and father, Charlotte would have become Queen in the 19th Century, instead of Victoria but she died in childbirth at the age of 21.

The succession then passed to George III’s fourth son, Prince Edward the Duke of Kent and the father of Victoria.

Danny Curran, founder and managing director of Finders International, says: “We’re delighted that absolute primogeniture replaced the old-fashioned male preference rule, and has changed centuries of history.

“The Windsor family tree is well documented, but we find all family trees fascinating. No matter how ‘ordinary’ the family, each tree reveals history, cultural and societal connections, memories and documentation of what makes a family.”