Prince Harry, Prince William and Princess Eugenie on what their grandmother the Queen is really like

The Queen is marking her 90th birthday with a host of celebrations, plus a highly anticipated ITV documentary titled Our Queen at Ninety, through which fascinating anecdotes of life with Her Majesty have already been revealed.

Kate has shared intimate details in her interview, like the monarch's delight over Princess Charlotte's arrival,what her son Prince George calls his great-grandmother and even the homemade treat she personally confected as a Christmas gift for her royal grandmother-in-law. Other members of the family are also sharing stories about the Queen, not as Britian's longest-ruling monarch but as a grandma!

TAP FOR THE QUEEN'S SWEETEST PICS WITH HER ROYAL GRANDCHILDREN "A lot of people get nervous around her... I've seen people literally faint in front of her," says Prince William

Grandson Prince William, 33, pays tribute to his grandmother by saying: "Growing up, having this figurehead, having this stability above me has been incredible. I have been able to explore, understand, slightly carve my own path. I greatly appreciate and value that protection."

The Queen and two future Kings – William and George – share a moment on the Palace balcony.

As for how members of the public react to meeting his grandma, he added: "A lot of people get very excited and sort of nervous around her. And I've seen some very comical moments. I've seen people literally faint in front of her. It's quite a startling moment as to what to do when you faint in front of the Queen! There's a lot of trembling knees and people can't talk sometimes. It's quite difficult talking to people when they can’t talk. You don't get very far; I don't get past the 'Hellos.'"

"I've been asking her what her secret is for years," quips grandson Harry, seen here giving Her Majesty a kiss.

His brother Prince Harry, 31, praised Queen Elizabeth's devotion to her duties and to the Commonwealth – whose membership has grown to 53 nations during her reign.

He said: "I look at the Commonwealth and think, 'Look how much it's achieved'... She should be incredibly proud of what she's led and what she’s achieved and what she's created amongst a huge amount of people from different ethnic backgrounds, different skin colors, different experiences, different islands – whatever it be. Hats off to her, it's incredible."

Prince Harry, second from right, famously broke out into laughter when his grandmother passed by during an official inspection at his military academy, Sandhurst.

The Queen made her first visit to a Commonwealth country – South Africa – in 1947, where she celebrated her 21st birthday and made her historic broadcast pledging her "whole life, whether it be long or short" to her people.

Harry noted: "It's just incredible to know that someone at that age appreciated and understood exactly what was expected of them and to basically put duty ahead of everything else so early on in her life is quite remarkable." He joked: "I have been asking her for years what her secret is, but she won't tell me."

Granddaughter Princess Eugenie says her Granny is happiest at her Balmoral estate in Scotland.

Princess Eugenie, the 26-year-old daughter of the Queen's son Prince Andrew and his ex-wife Sarah, Duchess of York, talks in the documentary about how "Granny" can truly be herself on her beloved Scottish estate, Balmoral. "It's the most beautiful place on Earth," said Eugenie. "I think Granny is the most happy there, I think she really, really loves the Highlands… Walks, picnics, dogs – a lot of dogs, there's always dogs! – and people coming in and out all the time.

Queen Elizabeth and the Duke of Edinburgh surrounded by their family, including Princess Eugenie to her left.

"Family-wise we're all there, so it's a lovely base for Granny and Grandpa to be – for us to come and see them up there, where you just have room to breathe and run."

Of her grandfather, the Duke of Edinburgh, Eugenie added: "I think Grandpa is incredible. He really is strong and consistent. He's been there for all these years, and I think he's the rock, you know, for all of us."

The Queen has a total of eight grandchildren: Prince William, 33; Prince Harry, 31; Peter Phillips, 38; Zara Tindall, 34; Princess Beatrice, 27; Princess Eugenie, 26; Lady Louise Windsor, 12; and eight-year-old James, Viscount Severn.

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