Downing Street is set to announce the new head of the UK civil service this week amid reports that the former private secretary to the Duke of Cambridge will be appointed to the role.
The Financial Times said Simon Case, 41, would be named as the UK’s top civil servant.
Mr Case spent almost two years working as William’s right-hand man before temporarily moving to Number 10 earlier this year to assist with the coronavirus response.
The newspaper said the appointment was confirmed by three people with knowledge of the selection process.
"An official announcement on the new Cabinet Secretary will be made on Tuesday, September 1," a Cabinet Office spokesman said.
Sir Mark Sedwill announced he was stepping down from the role in June.
Announcing the news after more than 30 years in Government service, Sir Mark, 54, said it had been "a privilege to serve".
He said: “I am fortunate to have served in some of the most challenging and rewarding jobs in national and international public service under seven prime ministers and in extraordinary times."
Prime Minister Boris Johnson paid tribute to Sir Mark saying: "Over the last few years I have had direct experience of the outstanding service that you have given to the Government and to the country as a whole.
"It has been by any standards a massive contribution – but as PM I have particularly appreciated your calm and shrewd advice.
"You have also spoken with a unique authority – unusual in a Cabinet Secretary – on international affairs and national security; and as National Security Adviser you have done much to keep this country safe."
He continued: "After serving for decades with great distinction – and unflappable good humour – I believe you have earned the gratitude of the nation."
Sir Mark will be paid £248,000 in "compensation" after he agreed to step down "early" from his senior position.
The advice was made by the Cabinet Office permanent secretary Alex Chisholm and was accepted by the Prime Minister.
The payment is likely to come "in the form of a pension contribution".
The civil service advertised for a replacement cabinet secretary with a proposed salary of £200,000.
