Charles will be joined by Queen Camilla and the Prince and Princess of Wales for the annual Commonwealth Day Service at Westminster Abbey.
Ahead of VE Day on May 8, Charles will say in his speech today: "This year, the world reflects on the 80th anniversary of the end of World War Two.
"More than one-and-a-half million men and women who served during the war came from across the Commonwealth to support the United Kingdom and its allies. On this special anniversary, we remember with particular pride and everlasting gratitude the untold sacrifice and selflessness of so many from around our family of nations who gave their lives in that dreadful conflict."
The King will also speak of today's "uncertain times" - meaning ongoing wars in places including Ukraine and the Middle East. He will say at the service: "It is all too easy to believe that our differences are problems instead of a source of strength and an opportunity for learning.
"The Commonwealth's remarkable collection of nations and peoples come together in the spirit of support and, crucially, friendship.
"The Commonwealth's ability to bring together people from all over the world has stood the test of time." This year's theme is Together We T...