President Halimah Yacob has written to Britain's Queen Elizabeth, and Prime Minister Lee Hsien Loong has written to Prince Charles - the Prince of Wales - as well as Prime Minister Boris Johnson to convey their condolences on the death of Prince Philip, Duke of Edinburgh.

Prince Philip, the husband of Queen Elizabeth, died aged 99 at Windsor Castle last Friday.

President Halimah, in her letter to Queen Elizabeth, said she and her husband were deeply saddened by the news, and conveyed her condolences to the Queen and the people of the United Kingdom of Great Britain and Northern Ireland, on behalf of the people of Singapore.

"The Duke of Edinburgh was an exemplary role model for the British people, and served the United Kingdom selflessly and with honour for over six decades," Madam Halimah wrote.

"Singapore will always fondly remember the state visit by Your Majesty and the Duke of Edinburgh to Singapore in 2006, as well as the generosity and warmth His Royal Highness had shown to our former president, Dr Tony Tan, during Singapore's first-ever state visit to the United Kingdom in 2014.

"The many decades of public service of His Royal Highness will continue to inspire successive generations of young people, and live on in the memories of many around the world."

The letters from the Singapore leaders, dated April 10, were released by Singapore's Ministry of Foreign Affairs yesterday.

PM Lee, in his letter to the Prince of Wales, the eldest son of Queen Elizabeth and Prince Philip and heir to the throne, said he was saddened to learn of the death of his father.

"As we mourn his passing, we remember the significant and remarkable life that he had led, dedicated first and foremost to service to the United Kingdom and its people, as well as to the peoples of the Commonwealth and the world at large," PM Lee wrote.

"He had an indomitable spirit, fighting for peace and justice in the Second World War in his early years, and later steadfastly pursuing environmental causes, where he was well ahead of the times, and taking a close interest in sports and education.

"His selfless devotion to service has contributed much to advance and uplift the livelihoods of people in the United Kingdom and within the Commonwealth. We will also remember him for his steadfast support of Her Majesty The Queen."

PM Lee noted that one of Prince Philip's distinguished achievements was the creation of The Duke of Edinburgh's Award scheme more than six decades ago.

The awards have nurtured and empowered young people to gain the skills, confidence and resilience to become exceptional individuals who can make a difference and contribute to society. The scheme also inspired Singapore's own National Youth Achievement Award programme, which was launched in 1992.

"It was clear that the Duke of Edinburgh made education an utmost priority," PM Lee wrote, recalling that Prince Philip visited the National University of Singapore in 1972, and the United World College of South East Asia in 1989.

"He also met students from the Singapore Sports School during Queen Elizabeth's state visit in 2006, where I had the great pleasure to meet him," PM Lee wrote. "On behalf of the Government of Singapore, I extend to you my deepest condolences and sympathies for this immense loss. He will be remembered and missed."

In his letter to Mr Johnson, PM Lee extended his deep condolences to the British Prime Minister and his government.

PM Lee wrote of the Duke of Edinburgh: "His unwavering support of Her Majesty The Queen in fulfilling her role as head of the Commonwealth was evident in his multiple pioneering efforts. These include his project to empower the youth of the Commonwealth, through ground-breaking initiatives such as the Commonwealth Studies Conferences which enabled them to acquire the skills, self-confidence and resourcefulness to meet the challenges of the future.

"It is a testament to his foresight that these initiatives continue to support social progress for people across the Commonwealth to this day.

"We have warm memories of the Duke of Edinburgh's many visits to Singapore, both accompanying Her Majesty The Queen and in his capacity as a member of the royal family. His visits regularly featured tours to one of our nature and wildlife reserves and educational institutions. It reflected his lifelong support for environment and education causes.

"We recall his gracious opening of the Singapore Polytechnic, one of our oldest post-secondary institutions, during his first visit in 1959."

PM Lee added: "The Duke of Edinburgh's contributions to the Commonwealth and the furthering of close relations between our countries are part of his lasting legacy."