All five living former US presidents have paid tribute to the Duke of Edinburgh, who passed away on Friday at Windsor Castle.
There were 18 different US leaders during Prince Philip's lifetime, 13 of whom met the Queen during their time in office, beginning with President Harry Truman who met then-Princess Elizabeth in 1951.
The Duke accompanied his wife on almost all these occasions.
Jimmy Carter, the oldest living US president at 96, said in a tweet issued via the presidential library: "We are sorry to hear that Prince Philip, Duke of Edinburgh, has passed away."
Donald Trump, who met the Royal Family twice during his four years in office, including a state visit in 2019, said Prince Philip's death is "an irreplaceable loss for Great Britain, and for all who hold dear our civilisation".
He said the Duke "defined British dignity and grace" and "personified the quiet reserve, stern fortitude, and unbending integrity of the United Kingdom".
Mr Trump's predecessor, Barack Obama, said they were nervous of how to handle the "palaces and pomp" of the British monarchy during their visit, but the Queen and Prince Philip put them "at ease with their grace and generosity".
Mr Obama said: "Prince Philip, in particular, was kind and warm, with a sharp wit and unfailing good humour.
"It was our first introduction to the man behind the title, and in the years since, our admiration for him has only grown."
George W Bush and his wife Laura praised Prince Philip's "dignity" and "boundless strength" during his many decades as consort to the Queen.
"He represented the United Kingdom with dignity and brought boundless strength and support to the sovereign," the couple said.
"Laura and I are fortunate to have enjoyed the charm and wit of his company, and we know how much he will be missed."
Mr Bush added that he and his wife offer heartfelt condolences to the Queen and the rest of Prince Philip's family.
Bill and Hillary Clinton said they had enjoyed "every opportunity we had to visit" Prince Philip during their time at the heart of the US government.
The Clintons said: "Hillary and I mourn the passing of His Royal Highness The Duke of Edinburgh, and we join people from all around the world in giving thanks for his remarkable life of service.
"We enjoyed every opportunity we had to visit with him through the years and will always be deeply grateful for the kindness he showed us."
Current US President Joe Biden, who is reportedly due to meet the Queen in June, was among the first to express his sympathy, praising Prince Philip's life of "devoted public service".
In a message on behalf of himself and his wife Jill, Mr Biden said: "Prince Philip's legacy will live on not only through his family, but in all the charitable endeavours he shaped."
The couple' message added: "The impact of his decades of devoted public service is evident in the worthy causes he lifted up as patron, in the environmental efforts he championed, in the members of the armed forces that he supported, in the young people he inspired, and so much more."
Cover image: Prince Philip met former US president Jimmy Carter in London in 1977 (Picture: PA Images/Alamy Stock Photo).