The Duke of Cambridge has paid tribute to the Queen's life of service in a preface to a new biography of his grandmother.
William highlights the "example and continuity" set by the Queen during her turbulent reign, praising her as a "model for a life of service to the public".
He also reflects on her private character, noting her "kindness and sense of humour" and "love of family and home" in a very personal account.
Writing in the preface to Elizabeth II: The Steadfast, William reflects on the technological and social changes the 89-year-old Queen has witnessed since her birth in 1926.
He said: "I think I speak for my generation when I say that the example and continuity provided by The Queen is not only very rare among leaders but a great source of pride and reassurance.
"Time and again, quietly and modestly, The Queen has shown us all that we can confidently embrace the future without compromising the things that are important.
"From a personal point of view, I am privileged to witness the private side of The Queen, as a grandmother and great-grandmother.
"The Queen's kindness and sense of humour, her innate sense of calm and perspective, and her love of family and home are all attributes I experience first-hand."
William also pays tribute to his grandfather Prince Philip, 94, who he said had "devoted his life" to supporting the Queen.
He adds: "All of us who will inherit the legacy of my grandmother's reign and generation need to do all we can to celebrate and learn from her story.
"Speaking for myself, I am privileged to have The Queen as a model for a life of service to the public."
The biography was written by former home and foreign secretary Lord Hurd and will be published on August 27.