The Duke thanked the guests attending the £150 ticket event for not letting "a little rain spoil a good day out" and praised his "granny" as someone "we all look up to in good times and in challenging moments to set an example".
Peter Phillips, the Queen's grandson, masterminded the open air Patron's Lunch to mark the monarch's patronage of more than 600 charities and organisations.
Along with other senior royals, she joined the huge crowd for the Patron's Lunch - recognising her patronage of more than 600 organisations in the United Kingdom and around the Commonwealth.
Ala Lloyd, who is the creative director of the carnival parade, told the BBC the eras of the Queen's reign through the decades are being symbolised by different sections of the parade.
Queen Elizabeth II's birthday celebrations are ending with a massive street party on the road leading to Buckingham Palace, culminating a weekend of official events in Britain marking her 90th birthday.
The Duchess of Cambridge uncovered the royal secret to a group of guests at the Guildhall reception after the National Service of Thanksgiving for Queen Elizabeth's 90th birthday at St Paul's Cathedral.
Princess Charlotte made her official debut on the balcony as the Royal Family observed an RAF flypast.
William and Harry are also expected to take to the stage to pay tribute to their grandmother.
Thousands of revellers celebrating the Queen's birthday on The Mall made use of their ponchos as storm clouds gatecrashed the royal celebration.
It was the 13-month-old royal's first appearance in public since posing with the Queen and her other grandchildren and great-grandchildren for a special royal portrait in April - and featured her first ever royal wave.
Several guardsmen also took part in the Trooping the Colour, though some of them collapsed during the ceremony and were given first aid. It is this event which has been expanded this year.