Prince Charles has paid tribute to his "darling Mama" on her 80th birthday.
The "proud and loving son" thanked the Queen for the "many wonderful qualities she has brought to almost an entire lifetime of service and dedication".
The message was broadcast ahead of a private black-tie dinner for The Queen and close family at Kew Palace.
The event, which began with fireworks, marked the climax of the celebrations. Earlier The Queen met thousands of well-wishers at a walkabout in Windsor.
The Queen and Prince Philip arrived at Kew Palace in the Royal Botanic Gardens in Kew, west London, for the birthday dinner at about 2000 BST.
BIRTHDAY DINNER GUESTS
The Queen, Prince Philip
The Prince of Wales, Duchess of Cornwall, Prince William, Prince Harry
The Duke of York, Princess Eugenie, Princess Beatrice
The Earl and Countess of Wessex
The Princess Royal, Rear Admiral Tim Laurence, Peter and Zara Phillips
The Duke and Duchess of Gloucester (Queen's cousin and spouse)
The Duke and Duchess of Kent (cousin and spouse)
Prince and Princess Michael of Kent (cousin and spouse)
Princess Alexandra (cousin)
Viscount and Viscountess Linley (nephew and spouse)
Lady Sarah Chatto and Mr Daniel Chatto (niece and spouse)
The Queen and her guests enjoyed a three-course dinner which included delicacies from the Royal estates.
Hebridean smoked salmon, Juniper-roast loin of Sandringham Estate venison and birthday chocolate sponge cake filled with a Highgrove fruit filling, were among the delights.
Along with immediate family members, others in attendance at the dinner include The Queen's cousins, niece and nephew.
The Prince of Wales, Camilla and Prince Harry were the first to arrive, followed by the late Princess Margaret's children, Lady Sarah Chatto and Viscount Linley and their spouses.
Prince William, accompanied by his cousin Zara Phillips, turned up next as scores of schoolchildren waving Union flags cheered.
In his message, which was broadcast on TV and radio, Charles reminisced about life in the royal household as he was growing up and wished his mother the "happiest of birthdays".
Ahead of the Coronation, he said, he had vivid memories "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".
The heir to the throne also spoke about his separation from his parents as a child while they were away on overseas tours in the 1950s and his joy at being reunited with them.
"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," he said.
He concluded: "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 those years 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."
BBC News royal correspondent June Kelly said it was interesting he focused on his mother's absences abroad, because relations between the pair had been strained and Charles had reportedly said she had been remote.
The prince was "given to introspection and he would have put an awful lot of thought into this", she added.
"But at the end of the day it is just a very warm tribute to a mother on this landmark birthday."
Earlier, Charles thanked well-wishers at the Gordon Highlanders Museum, Aberdeen, which he was officially reopening after a £1.2m refurbishment.
During the informal walkabout in Windsor, the band of the Irish Guards played Happy Birthday and crowds of about 20,000 cheered.
The Queen - dressed in a vibrant pink coat and hat - accepted gifts, cards and flowers as she and Prince Philip walked around the town for 45 minutes.
The crowd unfurled Union Jacks and birthday banners over police security barriers.
Earlier in the day, some 300 well-wishers in New Zealand, the first Commonwealth country to celebrate the Queen's 80th, spelt out: "EIIR 80" on Government House's lawn, in Wellington.
Also among the birthday messages was a special visual tribute from 500 crew members of the Royal Navy aircraft carrier HMS Illustrious, who lined up in formation to spell out 'Happy 80th'.
And the Queen thanked the 40,000 or so people who had sent her cards and e-mails, saying they had helped make the day a "special one".
The Queen's birthday present from the Cabinet was a china tea set made by Spode pottery in Staffordshire.
The prime minister's official spokesman said Buckingham Palace had indicated it was "something the Queen specifically would like".