The death of Sultan Qaboos bin Said al Said sparked three days of national mourning, with a host of international leaders gathering to pay their respects at his funeral.
William added: “I was truly honoured to spend time with His Majesty during my visit to Oman last month. It was clear from all those I met that he will be remembered with great affection.
“His Majesty was unwavering in his commitment to improve the lives of his people, and in his resolve to work towards regional stability.
“I am thankful for His Majesty’s many years of friendship with my family and the UK.
“I offer my heartfelt condolences to the Omani people, and wish to send a personal message of friendship as Oman mourns the death of His Majesty,” he concluded.
Wills’ heartfelt message comes after his recent visits to Kuwait and Oman in December.
An official statement from Kensington Palace in early November revealed the details of Wills’ trip to the Middle East.
“Throughout the tour, The Duke’s programme will pay tribute to the historic ties Britain shares with Kuwait and Oman, and will highlight strong links and cooperation in many areas, including education, the environment, and defence,” the message stated at the time.