The Prince of Wales has thanked British troops based roughly an hour's drive from the Ukrainian border for "defending our freedoms" as he kicked off a surprise trip to Poland.
William told soldiers at an air defence military base in the south-eastern Polish city of Rzeszow that their work to keep "an eye on" the situation in Ukraine is "really important".
After arriving at the base this afternoon, the Prince, dressed casually in a black puffer jacket and trousers, was shown the new 'cutting-edge' air defence system, Sky Sabre.
Prince William said the two-day trip will allow him to personally thank troops and pay tribute to the "inspiring humanity of the Polish people" aiding Ukrainian refugees.
Speaking to the soldiers, he said: "I just wanted to come here in person to say thank you for all that you're doing, keeping everyone safe out here and keeping an eye on what's going on.
"So, just a big thank you for what you do on a day-to-day basis."
He added: "You're doing a really important job out here and defending our freedoms is really important, and everyone back home thoroughly supports you."
The base, made up of a coalition of British, Polish and US troops, is helping to aid support to Ukraine.
Major Richard Kaye, who met the Prince, said: "We're here to protect critical national infrastructure in the region.
"We're absolutely privileged to host His Royal Highness the Prince Of Wales and privileged that he's chosen to come and visit us."
William also visited Polish soldiers at the 3rd Brigade Territorial Defence Force base in Rzeszow.
On arrival, the Prince was greeted by Poland's defence minister and deputy prime minister Mariusz Blaszczak.
Mr Blaszczak expressed his gratitude for the co-operation between British and Polish troops.
William was then shown a Polish self-propelled howitzer artillery system that had a British turret.
Major Przemyslaw Garema, 35, a professional soldier in the brigade, said: "It is very important equipment which Poland donated at the beginning of the war to the Ukraine, we delivered a few batteries then.
"We have been training the Ukrainian soldiers in order to teach them how to use this."
William will later travel to an accommodation centre in Warsaw to meet Ukrainian refugees who have fled and found sanctuary in the Polish capital.
Landing in Warsaw, the Prince said: "It's fantastic to be back in Poland.
"Our nations have strong ties. Through our co-operation in support of the people of Ukraine and their freedom, which are also our freedoms and yours, these ties are further strengthened.
"I'm here because I want to personally thank the Polish and British troops working in close and crucial partnership.
"I also want to pay tribute to the inspiring humanity of the Polish people. You have opened your hearts as much as your homes.
"That's why, this afternoon, I visited Rzeszow to meet troops based there to hear their stories and recognise their duty.
"I was struck by their passion as well as their shared determination to defend our shared freedoms."
The accommodation centre houses about 300 women and children who have arrived in the country recently, providing residents with two meals per day, and offers Polish language lessons, employment support, a children’s play area, psychological support and kickboxing classes.
William will hear from residents about their experiences before meeting volunteers.
He spoke of wanting to "underline" his continued support and gratitude to the Polish people.
On Thursday, the Prince will meet Polish President Andrzej Duda at the Presidential Palace and visit a local food hall to speak with Ukrainian refugees.
He will also lay a wreath at the Tomb of the Unknown Soldier, a monument dedicated to Polish soldiers who lost their lives in conflict.
The late Queen Elizabeth II and the late Duke of Edinburgh laid a wreath during their state visit to Poland in 1996.
It is William's first trip to Poland since he visited in 2017 with his wife the Princess of Wales.