The Queen admires the Duchess of Cambridge for adoring her grandson Prince William as himself, and not his title, a royal expert has said.
Biographer Andrew Morton, who has penned books on Princess Diana and Meghan Markle, says the monarch also spends time nurturing and supporting their relationship.
William and Kate met as students at St Andrews University in Scotland - and at times had a rocky romance before tying the knot 11 years ago.
They now have three children Prince George, Princess Charlotte and Prince Louis - and have become a safe pair of hands for the monarchy.
And speaking to OK! magazine, Mr Morton said: "The thing about Kate is the Queen was impressed she adored and loved William for himself, not for his title.
"She spends a lot more time supporting and nurturing the relationship between William and Catherine than she did with Charles and Diana. It's pretty clear she wasn't going to make that mistake again.
"Everything that happened in [Kate and William's] relationship was quite strategic, quite thought through, after a period of time. In the beginning, nobody in the royal household expected for a second that the university romance with Catherine and William would continue for any time after they graduated, like most college romances which disintegrate under the intense scrutiny of jobs and geography."
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His comments come following the release of his latest biography on the Queen, which is being released in her Platinum Jubilee year.
And in the book, simply titled The Queen, he reveals how the monarch was "positively playful" on William and Kate's wedding day.
He writes in the book: "The Queen was positively playful on the day of her grandson’s nuptials, ‘practically skipping’ according to one observer, absolutely thrilled at the way the public had reacted to the royal newlyweds.
"She had a sense that the future of the Royal Family, her family, was now secure. The monarchy was once again held in admiration and affection by the masses."
Now, 11 years on from that day, both Kate and especially William's royal responsibilities have increased markedly.
Two weeks ago, the second-in-line to the throne attended the State Opening of Parliament for the first time ever, accompanying his father Prince Charles and his wife Camilla.
Meanwhile, last week, he was also given the task of heading to the United Arab Emirates to pass on condolences on behalf of the Queen following the death of leader Sheikh Khalifa bin Zayed Al Nahyan.
It was the first time William has been asked to pass on the monarch’s condolences following the death of a foreign head of state.
