The annals of history are full of stories of forgotten royal siblings. They were the ones left out in the cold while their brothers and sisters prospered or ascended the throne. Thankfully, though, times have changed. But, that being said, Princes William and Harry have a stepsister whom few know about. And there are also good reasons why many haven’t heard of her, too. All in all, then, it’s a complicated but fascinating bit of royal history.