The Prince of Wales has paid a touching tribute to his mother, wishing her the "most special and happiest of birthdays".
Charles, at a beacon lighting ceremony at Windsor Castle to mark the Queen's 90th birthday, spoke of the "love and affection" for her throughout the country and the Commonwealth.
He called the head of state "Mummy" during his short address - often his affectionate introduction for the sovereign during royal celebrations.
As dusk approached on her milestone birthday, he said: "Your Majesty, Mummy, I find it very hard to believe you've reached your 90th year and I suddenly realised the other day that I've known you since you were 22 years old.
This is, ladies and gentlemen, a very special occasion and the beacon Her Majesty is about to light will also represent, as it lights other beacons across the nation, the love and affection in which you are held throughout this country and the Commonwealth.
"So, ladies and gentlemen, can we wish Her Majesty the most special and happiest of birthdays on this occasion. And long may you reign over us.
"Now, ladies and gentlemen, can I ask you as well if you could raise three very special cheers for Her Majesty on this special occasion.
"And if they're loud enough it might just work to light the other beacons by spontaneous combustion."
The Queen and the Duke of Edinburgh were driven to Cambridge Gate in Home Park, Windsor, for the lighting of the first in a network of more than 1,260 beacons.
She was dressed in a white silk headscarf for her last public engagement of the day before a private black tie dinner hosted by Charles in the Waterloo Chamber of the castle.
Charles handed the torch to the Queen and invited her to light the principal beacon - a large brazier on a 20ft (6m) pole at the start of the Long Walk.
With the beacon towering above them Charles handed a flaming torch to the Queen who lit a fuse which set off a series of small controlled explosions which ignited the beacon.
It took a while to get going and Bruno Peek, who has organised a number of national beacon lighting events to mark royal anniversaries, said Philip quipped: "It's not going up".