Margaret was interviewed by Duncan in the late 1960s and had a few sweet things to say on her older sibling.
"My sister has an aura," said Margaret, "I'm enormously impressed when she walks into a room. It's a kind of magic"
The princess also revealed that she was more than willing to help out, "In my own humble way I've always tried to take some of the burden off my sister."
"She can't do it all... and I leap at the opportunity to help. Sometimes it can be very formal and boring, but I've got a reflex against that now. It's very much up to one not to be bored."
Known for her sharp tongue, Margaret, who was 39-years-old during the interview, told Duncan that she had mellowed with age and was less inclined to give sneering looks.
"My friends used to tease me and call it my 'acid-drop' expression..."
Discussing the future success of the monarchy, the princess implied that it depended on the royal family raising "nicely brought up young people."
Princess Margaret passed away at the age of 71 during the Queen's Golden Jubilee year of 2002 after a period of ill health. Her life has been portrayed in Netflix's The Crown.