The King will describe this as "a time of great challenge" as "across the world, communities and nations face the increasing pressures of conflict" during his message to mark Commonwealth Day.
In an extract released ahead of the annual event on Monday, celebrating the Commonwealth nations, King Charles, who is also head of the Commonwealth, writes: "We join together on this Commonwealth Day at a time of great challenge and great possibility.
"Across our world, communities and nations face the increasing pressures of conflict, climate change and rapid transformation. Yet it is often in such testing moments that the enduring spirit of the Commonwealth is most clearly revealed."
It can be seen as a veiled reference to recent hostilities between US and Israeli forces and Iran, as well as conflicts from Ukraine to Sudan. Scientists also designated 2025 as the third warmest year on record, with the climate crisis a long-held concern of the King.
But wanting to convey an optimistic tone and outlook about the role of Commonwealth nations, he also writes: "Working together, we can ensure that the Commonwealth continues to stand as a force for good - grounded in community, committed to the kind of restorative sustainability that has a return on investment, enriched by culture, steadfast in its care for our planet, and united in friendship and in the service of its people."
Commonwealth Day will be marked by an annual service at Westminster Abbey on Monday attended by senior members of the Royal Family, leading politicians and diplomats among a congregation of 1,800.
Charles and Camilla will be joined by the Prince and Princess of Wales, as well as the Princess Royal and her husband, Vice Admiral Sir Tim Laurence.
Read more from Sky News:
Ian Huntley dies after prison attack
Indonesia to ban social media for under-16s
At least 10 killed in missile strikes in Ukraine
It will be the first significant gathering of senior members of the royal family since the arrest of Andrew Mountbatten-Windsor.
Spice Girl Geri Halliwell-Horner, an ambassador for the Royal Commonwealth Society which stages the event, will give an address, and there will be a reflection from former Strictly Come Dancing judge Oti Mabuse and a poem from Selina Tusitala Marsh, the inaugural Commonwealth poet laureate.
As head of the Commonwealth, Charles has followed the tradition set by Queen Elizabeth II of issuing an annual message to the 56 member nations.
In November, the nations will hold their biennial Commonwealth heads of government meeting in St John's, the capital of Antigua and Barbuda.
(c) Sky News 2026: King Charles will make veiled reference to Iran War in Commonwealth Day message
Soham murderer Ian Huntley dies after prison attack
Donald Trump's war with Iran is going global - this is a chaotic and dangerous moment
41 dead in clashes after 'disguised' Israeli commandos dig up grave searching for missing navigator
Boy, 7, dies after being struck by car in Staffordshire
Two children among at least 10 dead in Russian missile strikes in Ukraine
Nigerian soldiers 'kill 45 bandits' in gun battle in Katsina
Kemi Badenoch accused of insulting armed forces for saying RAF 'hanging around' in the Middle East
'I stabbed a teenager in the neck - here's my message for people who carry knives'