The Queen has expressed her sadness following the death of the Emir of Kuwait Sheikh Sabah Al Ahmad Al Sabah, saying she deeply valued his friendship towards the UK.
In a message to his successor Sheikh Nawaf Al Ahmad Al Sabah, who has been sworn in as the ruler of the tiny oil-rich country, the monarch praised the late emir's humanitarian work.
The Queen wrote in the condolences, which were also shared on the royal family's official Twitter account: "I was saddened to hear of the death of His Highness Sheikh Sabah Al Ahmed Al Jaber Al Sabah.
"Your distinguished brother devoted his life to the service of the State of Kuwait and especially its relationship with its allies and friends.
"He will be long remembered by all who work for regional stability, understanding between nations and between faiths, and for the humanitarian cause.
"I have deeply valued his friendship towards the United Kingdom, and his memorable State Visit in November 2012.
"I offer Your Highness my sincere condolences. I offer also my sympathy to the people of Kuwait.
"May the long history of close companionship between our two families continue."
The message was signed Elizabeth R, and accompanied on social media with a photograph of the Queen alongside Sheikh Sabah at Windsor Castle during his 2012 state visit.
The 91-year-old ruler, who has been hailed as a great humanitarian leader, died in hospital in the United States on Tuesday.
His coffin will be flown back to Kuwait from Rochester, Minnesota, home of the Mayo Clinic where he had been receiving medical treatment after falling ill in July.
His funeral would typically draw tens of thousands of mourning Kuwaitis and scores of foreign leaders and dignitaries but, because of the coronavirus pandemic, his burial will be a private family service instead.
As ruling emir, he faced falling oil prices, internal political disputes and the fallout from the 2011 Arab Spring, but he will be known for resolving regional disputes including the ongoing deadlock between Qatar and other Arab nations.
At 83, Sheikh Nawaf is not expected to deviate from the diplomatic path charted by his half-brother, but his accession has sparked speculation about who will become the next crown prince in Kuwait, which is known for its lively elected parliament and relative independence in a region of Gulf Arab monarchies.