The Queen’s official birthday is being marked with the annual Trooping the Colour parade.
She is being joined by members of her family and thousands of spectators to watch the display in Horse Guards Parade in Whitehall.
The Prince of Wales, the Duchess of Cornwall, the Duke and Duchess of Cambridge and the Duke and Duchess of Sussex are all attending.
The Queen celebrated her 93rd birthday in April.
The royal colonels – the Prince of Wales, colonel of the Welsh Guards, the Princess Royal, colonel of the Blues and Royals, the Duke of Cambridge, colonel of the Irish Guards and the Duke of York, colonel of the Grenadier Guards – are all riding on horseback as part of the parade.
The Duchess of Sussex made her first appearance in public since giving birth to her son Archie four weeks ago.
The Duke of Edinburgh, who celebrates his 98th birthday on Monday, has retired from official public duties and is not attending.
The Queen watched the ceremony – which this year parades the flag from the 1st Battalion Grenadier Guards – from a dais in Horse Guards Parade and she also inspected the lines of guardsmen.
Among the guests was Theresa May, who formally stepped down as prime minister on Friday, but will remain in office until a successor has been appointed.
The Royal Family then returned to Buckingham Palace, where gathered on the balcony ahead of the RAF flypast.
More than 20 aircraft will take part including modern jets and historic aircraft, with the Red Arrows as the finale.
Following the parade, which involved about 1,400 soldiers, the King’s Troop Royal Horse Artillery fired a 41-gun salute in Green Park.
Trooping the Colour originated from traditional preparations for battle and has commemorated the birthday of the sovereign for more than 250 years.
Colours, or flags, were carried, or “trooped”, down the rank so that they could be seen and recognised by the soldiers.