The Duke and Duchess of Cambridge's wedding day was not just a happy occasion for the loved-up couple's family and friends.
Millions of people around the world tuned in to watch the future king finally marry his university girlfriend in a romantic ceremony at Westminster Abbey.
Kate wowed in her stunning Alexander McQueen wedding dress and royal fans at Buckingham Palace cheered loudly when they appeared on the balcony and shared two kisses.
And according to a new book, it wasn't just the newlyweds who were left overjoyed by the big day - the Queen was too.
Royal author Andrew Morton, best known for his 1992 biography of Princess Diana, has written another biography - this time of the Queen in her Platinum Jubilee year.
And in the book, simply titled The Queen, he reveals how the monarch was "positively playful" on her grandson'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."
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And now, 11 years on from that day, both Kate and especially William's royal responsibilities have increased markedly.
Last week, 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.
It was announced that William would attend the ceremony after the Queen reluctantly pulled out on the advice of royal doctors due to her continued mobility problems.
During the event, William took his place in the procession behind the Imperial State Crown and sat at the side of Charles, who had the responsibility to read the Queen's speech.
Meanwhile, earlier this 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.
And for the Mirror's royal editor Russell Myers, it shows how William is being primed already to be a future king.
He said: "William is emerging as a trusted lieutenant of the Queen, especially over the last couple of years.
"With the ongoing Sussex saga and the tawdry scandal surrounding his uncle Prince Andrew, William has been involved in top-level conversations regarding their futures, so it shows it is not just Charles but William also being prepared for kingship.
"Charles has often been realistic in accepting his reign most likely will be short-lived in comparable terms.
"He is fully supportive of William being his understudy and learning the ropes with him in order to shore up all of their futures."
The Queen by Andrew Morton, published by Michael O'Mara, is available on May 24.
