AceShowbiz -

Demi Lovato has canceled her scheduled appearance at Philladelphia Fourth of July Jam due to strep throat. The free concert to celebrate the country's Independence Day will continue with country singer Hunter Hayes replacing the "Heart Attack" singer.

Desiree Peterkin-Bell, a city spokeswoman, said that she and people in the city were sad Lovato couldn't take the stage at the event, but were "excited" to have Hayes. "Hayes is one of the biggest stars in country music right now and we know that he will be a great addition to the stellar lineup we already have in place!" Bell said.

Hayes is set to join other performers, including John Mayer, Ne-Yo, J. Cole, Jill Scott, Grace Potter, Ben Taylor and The Roots. Hosted by comedian Kevin Hart, the event will be closed with an incredible fireworks finale over the Philadelphia Museum of Art.

As for Lovato, before canceling her appearance, the 20-year-old singer took to Twitter to inform fans that she was feeling unwell. "Chills + fever + gross looking tonsils... = no bueno... Mooooommmmmm????!!!!!" she tweeted on Tuesday, July 2. "Sucks being so sick when you're alone and away from home. someone... come hold meeeeee... And bring me soup!!!"

On Wednesday, June 3, she tweeted again, "I can't sleep cause my throat hurts!!!"