The royal couple had a particularly busy schedule over the extended Jubilee weekend, greeting royal fans across the country. On Sunday evening, they could be seen enjoying the Platinum Jubilee Pageant with their children.
Before this, they made what is suggested to have been an off-the-cuff visit to a street party in London to meet celebrators.
It is understood the Duke and Duchess of Cambridge dropped in “informally” to a do in the Ladbroke Grove area.
This is close to their home, Kensington Palace.
The pair said hello to residents and thanked them for joining in with the celebrations for the Platinum Jubilee.
Many thousands of such street parties were taking place at the same time across the country.
More than 16,000 of these were approved by local councils in England alone, according to the Government.
Hertfordshire County Council received a record 475 applications and chose to waive usual rod closure fees.
A source said the Cambridges’s street party visit was a last-minute addition to their Jubilee programme.
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Kate also visited Cardiff Castle along with Prince William and their two oldest children over the weekend, where they were shown rehearsal preparations and some of the other behind-the-scenes work that went into the Jubilee celebrations.
Concert producer Richard Perry, from Port Talbot, told the BBC the event at the Castle had been “building for the last three months”.
He added: “It was heightened once we heard that their royal highnesses were coming to visit the rehearsals.”
The Cambridges’s final Jubilee appearance was made at the close of the Pageant, when they stood on Buckingham Palace’s balcony alongside their children, Prince Charles and Camilla, Duchess of Cornwall and, of course, The Queen.
Following the long-weekend of events, Her Majesty said she had been “humbled and deeply touched that so many people have taken to the streets to celebrate my Platinum Jubilee”.
The Queen added: “While I may not have attended every event in person, my heart has been with you all; and I remain committed to serving you to the best of my ability, supported by my family.”