The Hollywood actress said that she studied hard to perfect her portrayal of Princess Diana, and found the interview scene one of the most challenging to perform.
"I watched [the Panorama interview] pretty much every day during make-up," said Naomi, speaking to Total Film. "I went running with it playing in my iPod.
"It was probably the thing I was most committed to getting exactly right — the head moves, the eye moves, the hair — because everyone knows it so well. It's such an extraordinary piece of TV."
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In the iconic interview, Princess Diana revealed that there were ''three of us'' in her marriage to Prince Charles. The biopic is believed to explore her relationship with the heart surgeon Hasnat Khan, with whom it was widely speculated that the people's princess had had a discreet romantic affair.
Naomi said that she was also worried about capturing Princess Diana's accent, and being able to copy her exact voice.
"I was very nervous about the accent," said Naomi. "She had a very distinct voice — she came from aristocracy so she was quite posh, but there was a warmth there, too. Her accent wasn't too 'fruity'.
The biopic focuses on the two years leading up to Princess Diana's death in August 1997. According to the filmmakers, it "charts how finding true personal happiness for the first time allowed [Princess Diana] to achieve her defining successes evolving into a major international campaigner and humanitarian".
Naomi has previously admitted that she was anxious about living up to the public's expectations and handling the royal's character with sensitivity.
"It was very scary going into it," she said, speaking at this year's Cannes Film Festival. "It was daunting because everyone feels they know her so well so you want to get it perfect. It's not an impression, it's an interpretation.
"It's also more complicated and sensitive when you take into account her two boys, William and Harry. I want to do her justice and help tell her story truthfully."
Diana will have its world premiere in London on 5 September before hitting cinema screens on 20 September.