Charles, who delivered the opening speech at COP21 in Paris in 2015, will speak to delegates gathered in Glasgow for the opening ceremony on Monday hosted by Prime Minister Boris Johnson.
During the day, a series of royal events in support of COP26 will be staged, while Charles, the Duchess of Rothesay and the Earl and Countess of Strathearn will join an evening reception the Queen will now not attend as she continues to rest.
The 95-year-old monarch was due to travel to Scotland for the high-profile engagement on Monday November 1.
However, a Palace spokesman said on Tuesday afternoon: “Following advice to rest, The Queen has been undertaking light duties at Windsor Castle.
“Her Majesty has regretfully decided that she will no longer travel to Glasgow to attend the evening reception of Cop26 on Monday, 1st November.
“Her Majesty is disappointed not to attend the reception but will deliver an address to the assembled delegates via a recorded video message.”
Charles will also co-host the Great Green Wall session, alongside French President Emmanuel Macron and his Mauritanian counterpart Mohamed Ould Abdel Aziz.
William and Kate will join Charles to host a reception for key members of his Sustainable Markets Initiative and winners and finalists from William’s environmental Earthshot Prize Awards.
The Queen faced preliminary tests in hospital on October 20 during her first overnight stay at a medical facility in eight years.
She has been resting following medical advice to cancel her two-day trip to Northern Ireland last week.