Queen's 'favourite' granddaughter's extraordinary way of learning her granny was monarch

She may be the monarch and is among the most famous and influential women in the world.

But to her eight grandchildren, the Queen is simply their grandmother and answers whenever they call her Granny.

But for one of her grandchildren, she didn’t quite realise that her Granny and the Queen are the same person - and she only found out in an extraordinary way.