Celebrations are taking place around the country on the day the Queen turns 90.
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 Prince of Wales recorded a special radio broadcast for the day, in which he read an edited passage from William Shakespeare’s Henry VIII.
On Twitter, the Queen thanked senders of “#HappyBirthdayYourMajesty” tweets.
In another tweet, the Queen said: “I send my best wishes to those who are celebrating their 90th birthday… on this shared occasion, I send my warm congratulations to you.”
The Queen, who was accompanied by the Duke of Edinburgh during her tour 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 on 9 September 2015 that the monarch broke the record held by her great-great-grandmother Queen Victoria, by being on the throne for 63 years and seven months.
Later on Thursday, the Queen will light symbolic beacons in Windsor.
In London, the King’s Troop Royal Horse Artillery staged a 41-gun salute at midday in Hyde Park. And the Honourable Artillery Company fired a 62-gun salute across the Thames from the Tower of London at 13:00 BST.
Prime Minister David Cameron said the Queen had been “a rock of strength for our nation” and the Commonwealth, 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.”
The reading by Prince Charles, which has been broadcast by the BBC, is an extract from a speech by Archbishop Thomas Cranmer to King Henry VIII after the birth of the future Queen Elizabeth I.