The King has praised the Ukrainian people for their "true valour" in a message marking the second anniversary of Russia's invasion.
Charles added he is "greatly encouraged" by the efforts of the UK and its allies in supporting Ukraine "at this time of such great suffering and need".
He said: "The determination and strength of the Ukrainian people continues to inspire, as the unprovoked attack on their land, their lives and livelihoods enters a third, tragic, year.
"Despite the tremendous hardship and pain inflicted upon them, Ukrainians continue to show the heroism with which the world associates them so closely.
"Theirs is true valour, in the face of indescribable aggression. I have felt this personally in the many meetings I have had with Ukrainians since the start of the war, from President Zelensky and Mrs Zelenska, to new army recruits training here in the United Kingdom.
"I continue to be greatly encouraged that the United Kingdom and our allies remain at the forefront of international efforts to support Ukraine at this time of such great suffering and need.
"My heart goes out to all those affected, as I remember them in my thoughts and prayers."
Mr Zelensky welcomed Western leaders to Kyiv on Saturday to mark the second anniversary of Russia's full-scale invasion.
The meeting comes as Ukrainian forces run low on ammunition and weaponry and foreign aid hangs in the balance.
Mr Zelensky posted a video from the Hostomel airfield together with Italian Premier Giorgia Meloni, Belgian Prime Minister Alexander De Croo and Canadian Prime Minister Justin Trudeau, as well as the the European Commission President Ursula von der Leyen.
"Two years ago, here, we met enemy landing forces with fire; two years later, we meet our friends and our partners here," Mr Zelensky said at the airport just outside of Kyiv, which Russian paratroopers unsuccessfully tried to seize in the first days of the war.
The Western leaders arrived shortly after a Russian drone attack struck a residential building in the southern city of Odesa, killing at least one.
Three women also sustained severe burns in the attack on a residential building Friday evening, regional Gov. Oleh Kiper wrote on his social media account. Rescue services combed through the rubble looking for survivors.
