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.
According to her mum Sophie, Countess of Wessex, 18-year-old Lady Louise Windsor had “no concept” that her grandmother, who she calls “grandmama”, was famous when she was younger.
Sophie, 57, told Sky News in an interview to mark the Queen’s 90th birthday: “I mean Louise had no concept really that the Queen and her grandmother were one and the same person.
“It wasn’t until she was at school that other children were mentioning it and saying, ‘Your gran is the Queen’.
“And she’d come home and say, ‘Mummy they say that Grandmama is the Queen.’ And I said, ‘Yes,’ and she said, ‘I don’t understand what they mean.’”
In the same interview, her dad, Prince Edward, also said he did not realise his mum was the monarch until the age of five or six.
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He said: “I can’t necessarily remember when that realisation was there.
“When you grow up in that family and in that environment, that’s just what your parents do.
“It’s been much more interesting watching our children growing up, and watching our children trying to work out what that this, and how that works. It was probably not until five or six I think.”
Lady Louise, who is currently studying for her A-Levels, largely grew up out of the spotlight and has a very close relationship with the Queen and the late Prince Philip.
She and her brother James are said to have spent a lot of time with their grandparents due to living close to Windsor and being around at a time when Her Majesty and the Duke of Edinburgh had largely stopped travelling internationally.
An insider previously told the Sun: "The Queen loves the fact that Louise and James relish their time at Balmoral, and she has become particularly close to Louise, who seems to have become her favourite grandchild, closely followed by James."
Now she's turned 18, Louise will now have a big decision to make - and it regards her title.
When she and her younger brother James were born, their parents decided against them using their HRH titles.
However, mum Sophie revealed in an interview last year they do indeed have the titles, and it will be up to them when they turn 18 if they want to use them.
Speaking to the Sunday Times, Sophie said: "We try to bring them up with the understanding they are very likely to have to work for a living.
“Hence we made the decision not to use HRH titles.
"They have them and can decide to use them from 18, but I think it’s highly unlikely.”
