With the final season of "The Crown" about to launch, focusing on Princess Diana's final days in the early episodes, the show's performance coaches have lifted the lid on how the cast perfect their portrayals.

As part of the research for the Netflix royal drama, William Conacher said he and cast members watched footage of the British royals with no volume to capture their mannerisms.

"First thing I say is nobody needs to do an impression and I don't believe anybody ever has on this show," Conacher, the supervising dialect coach, told Reuters.

"It's more about analysing what the face does, what the mouth does, what the head does, and then letting your voice come through that shape."

It is a strategy that has paid off. Claire Foy and Olivia Colman, who have played Queen Elizabeth at different periods of her life, have both picked up awards for their performances.

"If we're talking about the queen, if you don't open your mouth, if you don't let your lips move much at all, do not tense, just let there be very little distance," Conacher said.

"Diana opened her mouth quite a lot and she also spoke in a very minor key. These are all little things, but they're hints as to how you make your voice sound like that character without actually changing your voice."

Movement coach Polly Bennett worked with actors "on how their physicality operates" in each season.

"That can be everything from idiosyncratic movement… so that's the things that we might broadly understand as Diana's tilting head or Prince Charles' slight 'underneathness' of his head."

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Season 6, released in two parts on November 16 and December 14, begins in the summer of 1997 before Diana, the mother of Prince William and Prince Harry and first wife of now King Charles, was killed in a car crash at the age of 36.

Season 5 actors Imelda Staunton, Dominic West and Elizabeth Debicki reprise their roles as Elizabeth, Charles and Diana respectively.

"Working… with Imelda… this season was to both be talking… how the queen ages and what changes in her body which is everything from she starts wearing glasses and maybe she's walking a little bit slower," Bennett said. "But also looking at the history of the queen and knowing that whenever she walks somewhere, she always knows where she's going because somebody is telling her."