Historian Anna Whitelock says "brand Diana became bigger than that of the Royal Family."
The late princess became one of the most photographed women in the world and her husband Charles reportedly became jealous of the attention she received.
During her marriage and after her separation from Charles, Diana continued to attend high-profile events and had a circle of A-list friends from Elton John to Freddie Mercury.
Speaking on Yahoo UK's 'The Royal Box,' Anna says: “Harry and Meghan are in this situation where actually they are significant to the royal brand in terms of generating interest, but actually not significant to the monarchy in terms of its future.
“I think the line that they’re walking and going to have to walk very carefully is between royalty and celebrity.
“There is very much a sense with the instagram and the way in which they are cultivating themselves as a sort of social media couple, they may end up diverting too far away from the royal brand and become celebrities in their own right.”
Watch the full episode of Yahoo UK’s show ‘The Royal Box,‘ here.