David Cameron led tributes to the "extraordinarily talented" Conservative politician Sir Simon Milton who died suddenly at the age of 49.
Sir Simon was chief of staff to London Mayor Boris Johnson as well as Deputy Mayor for planning and previously led Westminster City Council.
The Prime Minister said he had been shocked and saddened by the news of the loss of a "much loved and much admired member of the Conservative family".
Expressing his sympathy to Sir Simon's partner Robert and his family and friends, he said he had been a "tower of strength" at City Hall.
Mr Johnson said the death had come as a "great shock", calling his chief of staff "a wonderful colleague and friend" who would be much missed.
"He was kind, he was decent, and he was universally acknowledged to be brilliant at his job," he said - highlighting his role in pioneering academy schools.
Sir Simon, who served a record eight years as leader of Westminster Council, was knighted for services to local government in 2006.
In 2007 he was elected chairman of the Local Government Association (LGA), the national voice of local authorities.
In the private sector Sir Simon also worked as the managing director of a public relations consultancy employing 40 people.
Mr Cameron said: "In all the years I have known him he was always kind, reliable, trustworthy and incredibly hard-working.
"He was in public life and public service for all the right reasons. He still had a huge amount to give and a great future ahead of him. He will be greatly missed."
Labour's former London mayor Ken Livingstone said that Sir Simon's death would be a sad loss to people from across the political spectrum.
"Although of course Sir Simon came from a different political background to me, I always enjoyed working with him because he was interested in what was best for Westminster and London.
"He was a distinguished and dedicated public servant who was respected right across London local government."Reuse content