The Queen is to lead the lighting of the principal Jubilee beacon in a special ceremony at Windsor Castle on Thursday evening, Buckingham Palace said.
The new engagement, added to the Queen’s jubilee diary, will see the monarch symbolically touch the Commonwealth Globe of Nations, created for the Beacons projects, in the castle Quadrangle.
This is the signal for the start of the illumination of the Tree of Trees principal beacon at Buckingham Palace
Waiting at the palace will be the Duke of Cambridge, representing his grandmother, as part of a special dual ceremony.
It comes as tributes continue to pour in for Her Majesty ahead of her Platinum Jubilee celebrations this weekend.
Princess Eugenie said, referring to her son August: “I think of my grannie and what she has stood for, for so many people and for our family during these 70 years.
“I’d love Augie to have her patience, her calmness and her kindness, while always being able to laugh at himself and keep a twinkle in his eye.”
She added: “Seventy years is really quite something, isn’t it?
“The Jubilee stands as a testimony to a woman who has transcended time and has been that constant rock for so many when the world can feel so fragile," she wrote in The Spectator.
The Queen, who at the age of 96 has mobility problems, returned to her Windsor Castle home with her dogs on Tuesday after a pre-Jubilee a break at Balmoral as she paces herself ahead of the four days of festivities.
The commemorations kick-start with the traditional Trooping the Colour military spectacle on Thursday, involving more than 1,500 officers and soldiers and 350 horses from the Household Division.
The Queen will lead the lighting of the principal Jubilee beacon
PA
Her Majesty is to celebrate her 70 years of reign this weekend
PA