Ukraine's president took time out from fighting back against Vladimir Putin's war to pay tribute to the Queen for her "selfless service to her people."
The leader wrote that her memory "will forever remain in the history of mankind".
Volodymyr Zelenskyy was among world leaders and major figures to pay their respects to Her Majesty as her coffin journeyed through Scotland to St Giles' Cathedral, Edinburgh, to Lie At Rest.
Ukraine's leader's tribute came as heads of states from across the globe prepare to fly in for the Queen's funeral in what is expected to become the biggest gathering of world leaders in decades.
Iconic world monuments - including the Burj Khalifa, the tallest in the world - were lit up in honour of Her Majesty, while a huge queue of well-wishers and mourners were seen outside the British embassy in Hong Kong waiting for hours to offer their condolences.
The Ukrainian president, spared the time from leading his country through war - as troops take part in a major counter-offensive against Russia's forces - to sign a book of condolence for the Queen.
His message read: “On behalf of the people of Ukraine and myself, I express sincere condolences over the death of Her Majesty Queen Elizabeth II.
“Ukrainian women and men share this great loss.
“We mourn with the United Kingdom, the Commonwealth of Nations and all subjects of the British Crown.
“The memory of Her Majesty and her selfless service to her people will forever remain in the history of mankind.”
Melinda Simmons, the UK’s ambassador in Kyiv, said she was “deeply honoured” by the president’s gesture.
“Grateful to the president for taking the time to do this given all else that is happening in (Ukraine) at this time,” she said.
She had last week shared an image of flowers left outside the embassy and thanked Ukrainian well-wishers, adding: "Amid an invasion, so much kindness and sympathy."
Elsewhere, a queue "hundreds of metres long" was seen snaking round the British consulate in Hong Kong.
A journalist for AFP reported seeing more than 1,000 people queueing for hours in the heat to lay flowers to the Queen.
Ambassadors and leaders from across the world shared photos of themselves signing the book of condolences - some with a photograph of the Queen by their side - while other lengthy queues were seen as far and wide as Rome, Italy to Manila, the Philippines.
People were also seen paying private and religious tributes to Her Majesty, with Sunday services in Pakistan and Cape Town, South Africa marking her passing.
The tributes came as presidents, prime ministers and crowned heads from across the globe prepare to fly to London for the Queen's state funeral on Monday, September 19, at Westminster Abbey.
The White House confirmed US President Joe Biden will attend with wife Dr Jill Biden, while Turkey's President Recep Tayyip Erdoğan and New Zealand Prime Minister Jacinda Ardern are among world leaders who have confirmed they will be there.
It is likely Westminster Abbey will see its capacity of 2,000 met.
Over the weekend, global monuments and iconic buildings were lit up in tribute to the Queen.
The Sydney Opera House and the tallest building in the world, Dubai's Burj Khalifa, projected large images of the Queen, while New York's Empire State Building shone and "sparkled" in purple and silver "to honour the life and legacy of Her Majesty, Queen Elizabeth II".
Berlin's Brandenburg gate and Rio de Janeiro's Christ the Redeemer lit up in the colours of the Union flag, the Eiffel Tower switched off its lights at midnight on Friday, and images of the Union and Israeli flags were projected on the walls of Jerusalem's Old City.