"I've been asked to speak at the Staples Center. I cannot be part of the public whoopla," Dame Elizabeth wrote on her Twitter page on Monday.
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"And I cannot guarantee that I would be coherent to say a word," she added.
The actress, and long time friend of the pop star, was devastated over Michael's death last week at the age of 50. Elizabeth wrote that she believes Michael would not have wanted her to share her continued sorrow in public.
"I just don't believe that Michael would want me to share my grief with millions of others. How I feel is between us," she Tweeted on Monday. "Not a public event."
Elizabeth, who like Michael, was thrust into the spotlight as a child star, said she has turned down the request to be at her friend's memorial out of her love for the star.
"I said I wouldn't go to the Staples Center and I certainly don't want to become a part of it. I love him too much," she wrote.
"My love goes out to Katherine and Michael's beloved children," she concluded.
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