Cyril Ramaphosa recalled the pair's rapport in a speech marking the end of his state visit to the UK.
He said: "We honour her, and we remember her very fondly – particularly for her wonderful relationship with the father of our nation, Nelson Mandela.
"Their relationship will forever be imprinted in our memory because they were very close. They were on first-name terms, and it was always a joy to listen to Nelson Mandela speaking about her very warmly and very fondly."
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