The Queen and her Buckingham Palace garden party guests will observe a minute's silence in memory of the victims of the Manchester terrorist attack.
On the lawns of the Queen's famous London home, thousands of people are expected to stand silently in tribute to the 22 people, including children, killed in the blast and the 59 injured.
The victims were targeted by a suicide bomber who detonated an improvised explosive device as young fans left a pop concert by US singer Ariana Grande at Manchester Arena.
The Queen is due to be joined at the garden party by the Duke of Edinburgh, Prince of Wales, Duchess of Cornwall, Duke of York and Princess Eugenie.
The minute's silence will observed just before the playing of the national anthem, which is normally held before garden parties begin.
In a message of support released earlier, the Queen said: "'The whole nation has been shocked by the death and injury in Manchester last night of so many people, adults and children, who had just been enjoying a concert.
''I know I speak for everyone in expressing my deepest sympathy to all who have been affected by this dreadful event and especially to the families and friends of those who have died or were injured."