Nelson Mandela felt so betrayed by Tony Blair's decision to join the US in invading Iraq he apparently launched a fierce tirade of criticism in a call to a Cabinet minister.
The criticisms were made in a formal call to Peter Hain's office
Peter Hain - a lifelong anti-Apartheid campaigner who knows the former South African president well - has claimed Mr Mandela was "breathing fire" down the line in protest in 2003.
He has said Mr Mandela felt any positive work done by Mr Blair's Government in Africa and elsewhere around the world had been "blown out of the water".
Because the criticisms were made in a formal call to the minister's office - and not in a private capacity - Mr Blair was informed.
He was virtually breathing fire down the phone on this and feeling a sense of betrayal. It was quite striking.Former Cabinet minister Peter Hain
"I had never heard Nelson Mandela so angry and frustrated.
"He clearly felt very, very strongly that the decision the Prime Minister had taken - and I as a member of the Cabinet had been party to - was fundamentally wrong.
"He was virtually breathing fire down the phone on this and feeling a sense of betrayal. It was quite striking."
Mr Hain, who grew up in South Africa, has published the revelations in a biography of Mr Mandela.
It comes as Mr Blair prepares to receive the Liberty Medal in the US later.
Awarded to figures who display leadership and advance the pursuit of freedom, it is being given to the former Prime Minister for his role in the Northern Ireland and Middle East peace processes.