Prince William, Prince Harry, the Queen Mum and Ali G

Prince William and Prince Harry revealed how the Queen Mum stunned a royal family Christmas dinner with her Ali G impression.

William and Harry told how she stood up at the end of the meal, did the Ali G trademark finger snap, and said: "Respec."

"It was two or three Christmases ago, and we were sitting down watching Ali G on TV," said William. "We were laughing when she came in. She couldn't understand what was going on, so we explained to her what he was doing. She saw Ali G click his fingers and say 'Respec', and Harry and I showed her what to do. She loved it, and after three goes she had it. Later that day, we were all in the dining room, having Christmas lunch, when she tried it out."

Prince Harry will never forget what she said to the Queen. He revealed: "It was at the end of the meal and she stood up and said, 'Darling, lunch was marvellous - respec', and clicked her fingers."

William said the entire family, including the Queen, burst out laughing.

But she couldn't get the hang of everything that was modern, he added. "I was given a mobile phone for Christmas and showed it to her," said William. "I invited her to press a few buttons and it kept blinking and flashing at her until she put it down and said, ‘I think I'd better leave that to you'.

"But she loved seeing what we got for Christmas and asking what was the latest, trendy thing."

William smiled: "She loved a good laugh, even if the joke was about her...Anything that was meant to be formal and went wrong, she enjoyed. She'd have a good giggle. She had such a young sense of humour. Every single thing was funny for any reason, she laughed herself stupid about it—it kept us all sane."

The Queen Mum also wanted to be kept up to date with all her great-grandsons' young pals and their lives at school.

"She loved to hear about all my friends and all they got up to, and relate it to her own youth," added William. "And she loved to hear about how much trouble I got into at school!"

The princes, who honoured Queen Elizabeth by walking behind her coffin during the historic ceremonial procession on 5th April 2002, also told how she had inspired them with her uncrushable independence.

Harry said: "She was determined to do things without help. She always wanted to walk up steps on her own. She was amazing. And she was very interested in everything we did, whether it was school or polo or anything."

William added: "I remember her as being a huge inspiration to me, someone to really look up to and admire.

"She was a historic link. I looked up to her because what an achievement it was to live to 101.

"It was a pleasure to sit next to her at lunch. She always had some great war stories and, to hear them from her, it really brought it all to life, something that happened long before we were born. She was incredible—nothing stopped her at all. Whenever I felt ill, I always used to remember that in the same circumstances she'd battle on, no matter how she felt. She never gave up."

William and Harry have spent the past week trying to comfort their heartbroken father Prince Charles. The family had been skiing in Switzerland when the Queen broke the news to them in a tearful phone call.

"They were very close," said William. "She gave him a lot of advice and help."

Harry added: "They always joked about everything. They both had the same sense of humour."

But there was an 80-year age gap between the Queen Mum and her great-grandsons—and one of their abiding regrets is they never had a chance to share with her a love of riding and fly fishing.

"By the time we were old enough to go riding with her, she'd stopped," added Harry.

But the boys' happiest memory of their great-gran was being there on her 101st birthday.

The entire royal family had assembled outside her London home, Clarence House, to greet loyal fans and watch a military parade.

William said: "Standing at the gates with your great-grandmother who is 101 years old as her troops go by was quite something."

His earliest recollections of the Queen Mother are at her home on the Queen's Balmoral estate in Scotland.

"My first memory of her was turning up at Birkhall and, as I was getting out of the car, I tripped and fell flat on my face right in front of her," he smiled. "I must have been about six or seven and she helped me up again. It was so funny because she was so old, and there was me being hauled off the ground by her."

But as William grew up, it became his turn to look out for his great-grandmother. "My favourite photograph of us together was a picture of me aged about nine or ten helping the Queen Mother up the steps at Windsor Castle," he said. I remember the moment because she said to me, `Keep doing that for people and you'll go a long way in life'."

William had lunch with the Queen Mother on the day he arrived at St Andrews University last September to start his history of art degree. She even made him late by laying on a such a massive spread at Birkhall that he couldn't get away on time.

Ali G, aka Sacha Baron Cohen, said: "A big shout out to da fallen leader of da Windsor massive. She woz always a hero in da ghettos of Berkshire. Me iz glad to ear I woz a influence on da Queen's Mum and not just on Prince Arry - who iz always bin one of me best customers."