Queen Camilla’s sister gave her honest opinion about her marriage to King Charles, calling the couple "polar opposites" in a new documentary.
Annabel Elliot, the Queen's sister, also called Camilla the King's "rock".
Elsewhere in the documentary, the Queen's close friend Lady Lansdowne described the couple's unbreakable "bond" as being strengthened by having to "fight" for each other.
Queen Camilla’s sister gives honest opinion about her marriage to King Charles: ‘They're polar opposites’
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She said: "I've known her a long time off and on. Her understanding of the role and how much difference it makes to the King has been absolutely outstanding," she said.
"This role is not something that she'd be a natural for but she does it really well.
"She provides that change of speed and tone, that's equally important."
The women were interviewed for tonight's BBC One royal documentary, Charles III: The Coronation Year.
Annabel Elliot [pictured] described Camilla as the King's 'rock'
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Elliot, who acted as one of Camilla's Ladies in Attendance on the day of the Coronation, added: "She is his rock, and I can't actually emphasise that enough.
"She's somebody who is completely loyal and she isn't somebody who has huge highs and lows."
The Queen's sister continued: "He brings to her everything.
"I'm not talking about all of this [referring to Buckingham Palace], but... he has such a knowledge and interest in so many different things, which she wouldn't really have been open to if she hadn't met him.
The new documentary will look at Charles and Camilla's Coronation in May
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Queen Camilla with Annabel Elliot and Fiona Lansdowne behind her at Coronation
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"They are yin and yang, really. They really are polar opposites. But I think it works brilliantly."
Elliot then commented: "Most of us as we get to this sort of age are thinking yes, quiet times. But theirs is just going to go like that."
Camilla's friend Fiona Lansdowne, one of her new Lady Companions, also said: "They are an extraordinary team.
"And I think it's, whether they've sort of had to fight to get there, or whether it's just because they've been through a lot together – it's made them have a really strong bond."