In the sixth and final series of the Netflix show, Diana (Elizabeth Debicki) - who helped landmine victims with her charity work - is seen on a yacht with boyfriend Dodi Al Fayed (Khalid Abdalla) explaining how survivors are often rejected by their communities because of the injuries they have sustained.
The late princess tells Fayed: "A man called Ken Rutherford drew my attention to it. He started the Landmine Survivors Network. After his jeep hit a landmine in Somalia he lost both of his legs.
"He said to me every survivor has a date of the day they stepped on the landmine. He said, 'Mine was December 16, 1963'. I said, 'Mine was 29 July, 1981 - my wedding day.'"
However, the royal biographer Ingrid Seward has dismissed the possibility of Diana - who was killed alongside Fayed in a Paris car crash in 1997 - making such a remark.
She told The Sun newspaper: "Diana would never have said anything like that. I think it is an unfortunate comparison.
"I think the mere fact 'The Crown' is depicting Diana's life and her death is exploiting her memory so they can put into her mouth anything that they want to - however distasteful people might find it."
Diana's work to ban landmines was influential and The Ottawa Treaty - banning the explosive weapons - was signed three months after her passing.
The royal writer added: "It was very important - it was her big thing and it was a great success too. It is something that she will always be remembered for."
The Netflix show, written and created by Peter Morgan, has already sparked debate by including scenes featuring Diana's ghost in the final season - of which the first four episodes will be released on the streaming service next week.