The majority of Britons only know a world in which Elizabeth II is queen, but the 90-year-old monarch’s recent poor health has many wondering what will happen in the event of her death or abdication. One thing that is almost certain is that Elizabeth II will be the last queen to sit on the British throne for a long time.

The prospect of a female monarch in Britain is certainly a lot more straightforward than ever before. After all, in the 12th century, England was plunged into a 19-year civil war over Henry I’s plans to install his daughter Matilda as the first female monarch. It would be the 16th century before England accepted its first female ruler.

The path for women became simpler still just three years ago with the passing of the Succession to the Crown Act. For the first time, it meant that the eldest child of the current monarch would succeed the throne, regardless of gender. Up to that point, it had always been the eldest male child that would be next in line.

With the act retroactively going into effect to take into account all those born in the line of succession after 2011, it meant that the first child of then Prince William would take the throne. Yet in 2013, William and the then-Duchess of Cambridge Kate Middleton gave birth to a baby boy, Prince George. Princess Charlotte was born two years later but the prospects of her taking the throne look slim.

Prince Charles is the first in the line of succession and would return a king to the throne for the first time since 1952. And it is highly doubtful that his wife Camilla Parker Bowles will even be given the ceremonial title of queen, due to her troubled relationship with the British public over their relationship while Charles was still married to Princess Diana.

William is next in line to the throne and his wife Kate would be expected to have the title of queen, although she would have no claim to the throne. In the event of William’s death or abdication, the title would pass to George. Only if George were to die or abdicate before fathering an heir, or were something to happen to that heir, would Charlotte be queen.

In that respect, Charlotte is in the same position as her uncle, Prince Harry, who has now been pushed down to fifth in line to the throne following the births of George and Charlotte. Harry has always seemed pretty happy about not having the extra responsibility. Asked about his prospects of being king during a visit to a school earlier this year, Harry joked, “You'll be glad to know, probably not!”

But a royal not expected to succeed the throne, or “spare heir,” as they are sometimes known, has become monarch before. Indeed, the last ruler before Elizabeth II was one such example. George VI only became king because his elder brother Edward VIII abdicated so that he could marry American divorcee Wallis Simpson.