The 74-year-old Absolutely Fabulous star said she had "not really" been following Meghan Markle and Prince Harry's exit to the US and subsequent tell-all interview with Oprah Winfrey.
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Asked if she would consider appearing in the Netflix drama, written by Peter Morgan and based on the lives of the Royal Family, she said: "No."
Lumley added: "I didn't watch it, or see it or do it. Lots of people love it and lots of people loathe it. It's mostly made up and lots of people don't know that it's made up – and I think that's awful.
"I put myself always in the shoes of the people – in this case the Royal Family – where people imagine how you speak to your husband.
"If you imagined how [husband] Stevie and I talk to each other and tried to write dialogue – it makes me feel faint with laughter!
"Well, some people say, 'Oh, everybody knows it's made up' – they don't, they think it's the truth.
"I couldn't watch it, because I feel if you don't agree with something, don't watch it and go: 'Oooh I hate that.' Just don't watch it."
Lumley has been married to conductor Stephen Barlow for 34 years.
The actress and political campaigner is a long-term friend of Prince Charles and was a guest at his wedding to the Duchess of Cornwall in 2005.
She played The Queen in 2013 in the BBC's adaptation of David Walliams's children's book Gangsta Granny.
Lumley told Jeremy Vine on Channel 5 earlier this month that she felt Meghan and Harry's interview had “spread a bit of unease and unhappiness just when we should be spreading unity and positivism and lots of love”.
She said: “It did seem to me a bit one-sided, because everybody knows that the Royal Family can’t really answer back.
“So I was anxious not to watch it actually. I didn’t want to watch the programme and didn’t watch the interview programme, but you can’t avoid it because everybody’s talking about it.”
Lumley added: “I feel terribly sorry about the whole thing. I’m so sorry for that family who we all love so much.”
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