Former Cabinet Secretary and head of the Civil Service Sir Jeremy Heywood has died from cancer aged 56, Downing Street has said.
Prime Minister Theresa May said Sir Jeremy “worked tirelessly to serve our country” and said his death was “a huge loss to British public life”.
Sir Jeremy, who died on Sunday morning, was diagnosed last summer and received treatment while continuing to work.
He stepped aside in June while he underwent treatment for the cancer and a related infection before formally retiring last month.
Sir Jeremy was appointed Cabinet Secretary in 2011 and three years later also took on the role of head of the Civil Service. His full title was Lord Heywood of Whitehall.
Paying tribute, the prime minister said: "This is extremely sad news and all of my thoughts are with Jeremy’s family and friends.
"The many retirement tributes paid to Jeremy from across the political spectrum in recent weeks demonstrated his extraordinary talent supporting and advising Prime Ministers and Ministers, and leading the Civil Service with distinction.
"He worked tirelessly to serve our country in the finest traditions of the Civil Service and he is a huge loss to British public life.
"I will always be grateful for the support which he gave me personally and will remember his achievements across his career as we regret that he did not have the chance to offer his talents for longer in retirement.
"Jeremy will be sorely missed and I send my deepest condolences to Suzanne and the children and to all his family and many friends."
His wife Suzanne paid tribute to her husband, saying: "He could light up any room or conversation."
She described him as a "wonderful father" who gave their children "a mix of challenge, a little teasing, total devotion and deserved praise".
She added: "For me, he was my wonderful partner for 22 years. We shared everything and I will miss him more than I can say."
Number 10 confirmed there will be a private family funeral in the coming days and then a memorial service next year.
Tributes were paid across the political spectrum.