The world addresses her as Her Majesty, but outside of Queen Elizabeth’s family and closest friends behind closed doors, only one other person has ever been able to refer to the monarch by her first name.

According to Royal Commentator Richard Fitzwilliams (via Express UK), in public spaces, only one man was ever allowed to refer to her by her first name—without any formality and titles.

“[Nelson] Mandela was,” he told the publication. “He called her Elizabeth and his affection for her was warmly reciprocated. Her state visit to South Africa in 1995 when he was President was one of the highlights of her reign.”

The pair’s relationship was often noted for being extraordinary, and their cordiality was also reflected on in the book “Good Morning, Mr. Mandela,” a memoir by his personal assistant, Zelda la Grange. In her books, she revealed that the two not only referred to one another by first names, but the South African President also commented on her weight.

“On a visit to Britain, I was struck by the warm friendship between Madiba and the Queen,” she recalled. “’Oh Elizabeth,’ he would say when he greeted her, and she would respond: ‘Hello, Nelson.’ I think he was one of the very few people who called her by her first name and she seemed to be amused by it.”

On a separate occasion, he allegedly also said, “Oh Elizabeth, you’ve lost weight.”

Mandela was the only one who allegedly had the honor and privilege to refer to the Queen in such an informal manner, and it’s unlikely she allows anyone to have that courtesy now, besides members of her family—and only when they are behind closed doors.

Unfortunately, if that is the case, the Queen stopped having someone with whom she had a less formal relationship a few years ago. Mandela died in 2013 at the age of 95.

Queen Elizabeth II Queen Elizabeth II is seen at the Chichester Theatre while visiting West Sussex on Nov. 30, 2017, in Chichester, United Kingdom. Photo: Getty Images/Stuart C. Wilson