Nelson Mandela was on a first-name basis with Queen Elizabeth II, a rare privilege contravening royal etiquette, the late anti-apartheid hero's foundation said Friday, sharing anecdotes of their fond relationship.

Queen Elizabeth II, the longest-serving monarch in British history, died aged 96 in her Scottish summer residence on Thursday.

"By his own admission, Nelson Mandela was an anglophile, and in the years after his release from prison cultivated a close relationship with the Queen," the Nelson Mandela Foundation wrote in a statement, sending condolences to the royal family.

"They also talked on the phone frequently, using their first names with each other as a sign of mutual respect as well as affection."

Fondly known to South Africans as Madiba, Mandela spent decades in prison before leading his country from white minority rule to a multi-racial democracy. He died in 2013 aged 95.

Mandela thought it was important that the former colonial power should have cordial and productive relations with the newly democratic republic of South Africa, the Foundation said.

The non-profit Mandela founded to promote freedom and equality quoted him as saying at a 1997 banquet for Prince Charles — now King Charles III — of how he came up with a special name for the queen after she visited the South Africa two years earlier.

"As a token of our affection to Her Majesty, we conferred on her the name Motlalepula, because her visit coincided with torrential rains as we had not experienced in a long time," Mandela had said, describing the her visit as a "watershed".

In later life Madiba would often take pleasure in reminding interlocutors from Britain that South Africa had thrown off the colonial yoke – as well as in asking anyone who had visited Britain "And did you get to meet the Queen?", the Foundation said.