Rainy conditions have not dampened the spirits of guests at a picnic lunch in London - the last of the events for the Queen's official birthday.
Ponchos were handed to many of the 10,000 guests at the Patron's Lunch - who also received a hamper of food.
Members of the Royal Family walked down The Mall greeting guests in a "walkabout" lasting 30 minutes.
The Queen gave a speech and thanked everyone for the birthday wishes she had received during the year.
She said: "To everyone here today and those holding street parties elsewhere I would like to say thank you for the wonderful support and encouragement that you continue to give to me.
"I hope these happy celebrations will remind us of the many benefits that can flow when people come together for a common purpose as families friends or neighbours."
She ended with a joke: "How I will feel if people are still singing Happy Birthday in December remains to be seen."
Her grandson, the Duke of Cambridge, also gave a speech to the gathering crowds and said: "Thank you so much for showing that the great British public doesn't let a little rain spoil a good day out.
"It means so much to see everyone here today."
Following the open-air lunch and speeches, a carnival parade was held along The Mall.
The day's events - held to recognise the Queen's official 90th birthday and her patronage of more than 600 organisations in the UK and around the Commonwealth - were organised by the Queen's eldest grandson, Peter Phillips.
Security has been tight, and guests, who have all paid £150 each to attend, went through body scanners before taking a seat at the picnic tables, which were set up along The Mall.
In nearby St James's Park, families have also been eating their own picnics in honour of the Queen.
The Pickles family, who took cover underneath some trees, told the BBC: "It's wet but this is exciting."
Another family, who had travelled to London from Nottingham, said: "We're having a fabulous time. We love the Queen, happy birthday."
By Peter Hunt, BBC News royal correspondent
A carnival parade, a picnic and a prince.
William was on The Mall to praise the woman who was the focus of this celebration; the future king's words were directed at his monarch and his grandmother.
The Queen travelled, with her husband, in an open-top car, while William, Kate and Harry were in the vehicle behind. It was a notable image of the present and the future of the monarchy.
It was a notable image with a notable absentee: Prince Charles had chosen to miss the Patron's Lunch and instead attend a street party near his Highgrove home in Gloucestershire.
For a Queen, now 90, there will be ongoing adjustments made to her programme. Lifts will be used rather than flights of stairs; the length of visits will be not too long, and standing around will be kept to a minimum.
But, officials insist, Elizabeth remains this country's active and fully-engaged head of state.
Back at the Patron's Lunch one of the guests was Anne Nutt, who is involved with the scouts and was at the event as Harlow District Scouts in Essex had won the Queen's Award for Voluntary Services last year.
Looking at the large puddles in The Mall, Ms Nutt said: "I think today is absolutely marvellous and it's when the British people show their true colours - the true British spirit.
"People have come out from their warm, dry homes for four or five hours in the pouring rain.
"But it's been nice to meet people from other charities and the large number of ex-servicemen that are here."
Ala Lloyd, the creative director of the carnival parade, said beforehand that the eras of the Queen's reign through the decades would be symbolised by different sections of the parade.
"We've got a lovely Commonwealth theme in the 50s with a giant Royal Yacht Britannia, flower power in the 60s, animals and nature in the 70s and crazy neon business going on in the 80s, and embarrassing shorts," she said.
She said she was just trying to do something which was "affectionate and friendly".
What's in the hamper?
The hamper was put together by Marks and Spencer and contains:
- "Best of British" sandwiches
- Pembrokeshire chicken roulade with Wye Valley asparagus and minted Cornish potato salad
- Scottish Smoked Salmon mousse with hot and cold Sandringham oak-smoked Lochmuir salmon
- Cornish Cove mature cheese and Red Leicester with Scottish seeded oatcakes
- Mini piccalilli pork pie
- A raspberry royale featuring Norfolk Tulameen raspberries and a strawberry jelly, layered with a sponge and clotted whipped cream hand decorated with a chocolate plaque
- Two butterfly cakes - one vanilla sponge cake with strawberry frosting and a lemon cake topped with lemon frosting
- Windsor apple juice, Pimm's and water
While the main event takes place in London, smaller street parties are being held around the UK.
On Saturday, thousands of people turned out to watch the annual Trooping the Colour parade.
Dressed in a vivid lime green coat and matching hat, the Queen was escorted down The Mall in a horse-drawn carriage to the ceremony at Horse Guards Parade.
After the procession of more than 1,600 soldiers and 300 horses, she appeared on the balcony of Buckingham Palace with members of her family, including Princess Charlotte, for an RAF fly past.
Ninety-year-old Heather Gunner from Walton-on-Thames in Surrey, who will be among the guests attending the street party, spoke of her admiration for the monarch, remarking: "She's got a lot on her plate for her age."
Born in the same year as the Queen, she received a ticket to the festivities through the charity Friends of the Elderly.
"I have great admiration for the Queen. I really do," she said. "I think she's coped excellently."