Ms Rippon said: “Lady Diana was almost slumped in the chair, she was in new territory.
“She was out of her depth.
“Put any 20-year-old in front of a television camera and say this is an interview about what could be one of the most important days of your life and it’s going to be seen by hundreds of millions of people around the world, and there is this man standing behind the person interviewing you making sure you get it right.”
She added: “Crikey, anyone would be nervous.”
Diana’s marriage to Prince Charles was notoriously fraught with tensions and tragedy.
She reportedly had doubts about walking down the aisle before the “fairytale wedding” which was viewed by an estimated 750 million people worldwide.
“With the knowledge of hindsight you read so much more into body language, what was said, looks that were given, reactions,” Ms Rippon said.
“Maybe we should have read so much more into that five seconds at the end of the interview. It might have told us so much more about what was to come.”