The show called "Harmony: A New Musical," was set to open Wednesday night to a sold-out crowd at the National Yiddish Theatre Folksbiene at the Museum of Jewish Heritage in Lower Manhattan.
The show will still go on despite Manilow's positive test.
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Manilow called it possibly "the cruelest thing that has ever happened to me."
The singer has been developing the musical for 25 years.
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