Here is the full text of Prince Charles's tribute to the Queen:
It is hard to believe that my grandfather, King George VI, was the same age as I am now when he died, and that my mother succeeded him when so young - the same age, in fact, as my sons are now
An 80th birthday is a very special occasion for every family - an occasion for celebration, for giving thanks and for looking back.
As a child, I can just remember my great-grandmother, Queen Mary, at 80.
Then I recall so well the 80th birthday of my grandmother in 1980.
Now I find it hard to believe my own mother, the Queen, is today celebrating her 80th birthday.
And it gives me enormous pride to be able to congratulate her publicly in this way.
And to thank her, on behalf of us all, for the many wonderful qualities which she has brought to almost an entire lifetime of service and dedication to her country, family, to the realms, and to the countries of the Commonwealth.
It is hard to believe that my grandfather, King George VI, was the same age as I am now when he died, and that my mother succeeded him when so young - the same age, in fact, as my sons are now.
I have vivid memories of the Coronation - of my mother coming to say goodnight to my sister and me while wearing the crown so that she could get used to its weight on her head before the Coronation ceremony; of thousands of people gathered in the Mall outside Buckingham Palace, chanting, 'We want the Queen' and keeping me awake at night; of my parents being away for long, overseas tours during the 1950s, and of determined attempts to speak to them on the telephone in far-distant lands when all you could hear was the faintest of voices in a veritable storm of crackling and static interference.
The world in which my mother grew up, and indeed the world in which she first became Queen, has changed beyond all recognition
I remember too the excitement of being reunited with our parents when my sister and I sailed out in the then-brand new yacht Britannia, to meet them off Tobruk at the Commonwealth Coronation Tour in 1954 - a tour that had lasted over six months and taken in 13 countries.
And of course, there was the thrill of witnessing the entire Mediterranean fleet of the Royal Navy steam past the Royal Yacht at high speed with my mother and father waving to all the ships' companies from the afterdeck.
Now there is no doubt that the world in which my mother grew up, and indeed the world in which she first became Queen, has changed beyond all recognition.
But during all this, she has shown the most remarkable steadfastness and fortitude, always remaining a figure of reassuring calm and dependability, an example to so many of service, duty and devotion in a world of sometimes bewildering change and disorientation.
For very nearly 60 of 80 years, she has been my darling Mama, and my sentiments today are those of a proud and loving son who hopes that you will join with me in wishing the Queen the happiest of happy birthdays, together with the fervent prayer that there will be countless memorable returns of the day.