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The 79-year-old Nelson was scheduled to perform Saturday at a private home in Castle Pines Village, Colo. The benefit was for an organization that provides animal care and shelter in the Denver area.
The host of the fundraiser, Fred Bartlit, tells The Denver Post that he was informed that Nelson was taken to the hospital after having trouble breathing.
Representatives for Nelson couldn't immediately be reached for comment Sunday night.
Watch Willie Nelson's Video for "You Don't Know Me"
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