Hunter Hayes replaced Demi Lovato at the annual Philadelphia Fourth of July Jam. Lovato was stricken with a case of strep throat, and in the two days before the cancellation was announced she told her fans on Twitter: "Chills + fever + gross looking tonsils . . . = no bueno . . . Mooooommmmmm????!!!!!" She added: "Sucks being so sick when you're alone and away from home."

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