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The Queen's official birthday is being marked with a scaled back celebration for a second year due to Covid.
This year's Trooping the Colour will see a reduced parade in the grounds of Windsor Castle, rather than in central London, led by the Scots Guards.
In 2020 the event was cancelled due to the pandemic with a ceremonial tribute performed at Windsor by Welsh Guardsman and a band of the Household Division.
It comes ahead of the Queen hosting US President Joe Biden on Sunday.
The monarch's actual birthday is on 21 April but her official birthday is marked on the second Saturday of June each year.
It is traditionally celebrated with a military parade near Buckingham Palace in which the Household Division marches carrying a regimental flag, known as a colour.
This year will see F Company Scots Guards Troop the Colour of the 2nd Battalion Scots Guards through the ranks of guardsmen on parade.
media captionWhat is Trooping the Colour?
The celebration will be smaller than normal and has been dubbed a "mini" Trooping the Colour.
But the military officer in charge of planning the parade said his aim was to create a "memorable and uplifting day" for the monarch, who has been based at Windsor during the pandemic.
Lt Col Guy Stone said: "Last year we had 85 on parade, this year we've got 274, plus 70 horses, so we're really excited about the event having grown and getting us back to normal for next year we hope.
"It's been very challenging, but we like a challenge. Covid has got a lot to answer for in so many ways, it's made this difficult but what we want to do more than anything is give the Queen a memorable and uplifting day."
image copyrightPA Mediaimage captionThis year's Trooping the Colour will be on a smaller scale than normal
Lt Col Stone, who serves with the Welsh Guards, is Brigade Major Household Division and was also in overall charge of the military arrangements for the Duke of Edinburgh's funeral.
It is the first time the Queen's official birthday has been marked since the death of her husband earlier this year.
The event will end with a 41 gun salute and there will also be a flypast by the Red Arrows.
Official celebrations of a sovereign's birthday have often been held on a day other than their actual birth date, particularly when the actual birthday has not been in the summer, so that there is better weather for a parade.
Meanwhile, heroes of the pandemic have been among those to be honoured in the Queen's Birthday Honours, with vaccine developer Prof Sarah Gilbert and former chair of the vaccine taskforce Kate Bingham among those to be recognised.
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On Friday the Queen and other members of the Royal Family were in Cornwall as part of the G7 summit of world leaders.
The monarch joined the politicians for a dinner at the Eden Project.
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