The Mayor of London Ken Livingstone accepted the resignation of senior aide Lee Jasper today.
The move follows a string of claims about Mr Jasper's alleged misuse of City Hall funds.
The Greater London Authority insisted tonight that there was no foundation for the allegations against Mr Livingstone's adviser on race relations.
But it added that Mr Jasper had tendered his resignation after new claims today.
"The mayor has accepted it," a spokesman said.
The resignation comes after London's Evening Standard newspaper claimed today Mr Jasper had sent risque emails to a woman involved with organisations which received City Hall cash.
The Greater London Authority (GLA) spokesman paid tribute to Mr Jasper's achievements.
"The record of the GLA in dealing with racism in London has been outstanding," he said.
"Racist attacks have been reduced by more than a half in eight years, and last year racist attacks rose by 12% in the UK as a whole but fell by 14 per cent in London.
"Operation Trident, aimed against black gun crime, has been an outstanding success with the arrest of many dozens of criminals engaged with guns without a single shot being fired.
"The GLA is an exemplary authority achieving national recognition in the country in regard to equality and procurement.
"Lee Jasper played a leading role in regard to these, and no evidence has been presented for the criminal allegations presented by the Evening Standard.
"However, Lee Jasper has stated that in light of material published today that he has tendered his resignation. The Mayor has accepted it."