Celebrations are taking place around the country on the day the Queen turns 90, the BBC reports.
Crowds lined the streets in Windsor as the monarch took part in a walkabout, and royal gun salutes have been fired from each of the UK’s capital cities.
The Queen, who was accompanied by the Duke of Edinburgh during her walkabout in Windsor, was presented with a birthday cake at the Guildhall by the Great British Bake Off champion Nadiya Hussain, who had created an orange drizzle cake with a butter cream and marmalade filling.
The monarch unveiled a plaque marking The Queen’s Walkway – a 6.3km trail that links 63 significant points in Windsor.
The trail was designed to recognise the moment the monarch broke the record on 9 September 2015 held by her great-great-grandmother Queen Victoria by being on the throne for 63 years and seven months.
The Queen will light symbolic beacons in Windsor later.
The Queen had been “a rock of strength for our nation” and the Commonwealth, Prime Minister David Cameron said, as he and fellow politicians paid tribute in the House of Commons.
Mr Cameron said: “Her Majesty The Queen has lived through some extraordinary times in our world.
“From the Second World War… to the rations with which she bought the material for her wedding dress.
“From presenting the World Cup to England at Wembley in 1966 to man landing on the moon three years later.
“From the end of the Cold War to peace in Northern Ireland.
“Throughout it all, as the sands of culture shift and the tides of politics ebb and flow, Her Majesty has been steadfast – a rock of strength for our nation, for our Commonwealth and on many occasions for the whole world.”
Earlier, a photograph was released showing the monarch with young members of the Royal Family.
The image, one of three taken by celebrity photographer Annie Leibovitz, shows the Queen surrounded by her five great-grandchildren and her two youngest grandchildren.
The other Leibovitz photographs show the monarch walking in the grounds of Windsor Castle with four of her dogs and sitting with her daughter, the Princess Royal.