Yahoo Autos Princess Diana wasn't allowed to call Prince Charles by his first name until they were engaged
Princess Diana was only permitted to address Prince Charles as "sir" until they were engaged.
The princess wasn't supposed to call him by his first name, writes royal biographer Andrew Morton.
"In Prince Charles' circle this was considered the norm," Morton added.
It's been 40 years since Prince Charles and Lady Diana Spencer announced their engagement on February 24, 1981.
The couple's engagement interview was watched by royal fans worldwide, but some people may not know how formal the couple had been with one another until that moment.
According to Princess Diana's biography, "Diana: Her True Story," by Andrew Morton, she was required to call Charles "sir" when they were dating and was only allowed to address him by his first name when they became engaged.
"It was not until Lady Diana was formally engaged to His Royal Highness The Prince of Wales that she was given permission to call him 'Charles.' Until then she had demurely addressed him as 'Sir,'" Morton wrote in the book, which was first published in 1992.
While Diana also had an official title - she was formally known as Lady Diana until she got married - Charles used her first name.
