Tens of thousands of people converged on central London in bright sunshine to witness the centuries-old Trooping the Colour military parade.
The 96-year-old monarch’s appearance at the festivities for her record-breaking 70 years on the throne had been in doubt due to illness and recent mobility problems.
But dressed in dove blue, her hands clasped on a walking stick, she took a salute from mounted troops from the balcony of Buckingham Palace, under the fluttering royal standard.
The Mall below was awash with red, white and blue union flags, with some die-hard royal fans having camped for days to be in prime position for the display of pomp and pageantry.
But many acknowledged the coming end of an era.
“We know it’s a special occasion because it might be the last day we’ll see Her Majesty in a public event,” ambulance service worker Gilbert Falconer, 65, told AFP after travelling from Scotland.
Recognition of the queen’s unprecedented reign saw tributes from political and religious leaders from across the world, including the leader of pro-Irish nationalist party Sinn Fein in Northern Ireland.
Michelle O’Neill’s message, praising the queen’s “significant” contribution to the peace process would have been unthinkable before the 1998 peace deal that ended years of violence over British rule.
Sinn Fein was the political wing of the Irish Republican Army paramilitary group, which blew up the queen’s cousin, Lord Louis Mountbatten, in 1979.