Demi Lovato won't be performing at Philadelphia's Fourth of July show as planned due to an illness.

The 20-year-old has cancelled her appearance at the annual free concert on Thursday because of strep throat.

"I can't sleep cause my throat hurts," Lovato told a fan on Twitter on Wednesday.

On Tuesday she also tweeted, "Sucks being so sick when you're alone and away from home. Someone come hold me."

While Lovato will take time to recover, singer Hunter Hayes will replace her place at the concert.

A city spokeswoman, Desiree Peterkin-Bell, said that while they are upset not to have Lovato play, they are happy to have the 22-year-old country singer as a replacement, according to The Associate Press. He is "one of the biggest stars in country music right now," Peterkin-Bell said.

Hayes, who toured with Carrie Underwood in 2012, released his self-titled debut album a year prior. The album's second single Wanted, topped the country charts. The single also went platinum. The young star was also nominated for Best New Artist at the 2013 Grammy Awards. He was up against Alabama Shakes, The Lumineers, Frank Ocean and Fun. The latter won the award.

Other artists set to perform at the annual July 4 concert include John Mayer, Ne-Yo, J.Cole and The Roots. Kevin Hart, a Philadelphia native, will host the show, which will end with fireworks over the Philadelphia Museum of Art.

The comedian announced on Twitter on Thursday morning that he's on his way to his home city and will also surprise fans who go to watch his movie Let Me Explain in theaters.

The 33-year-old tweeted, "I will be making pop ups in random movie theaters through out the day."

The comedic film hit theaters on Wednesday and shows Hart as he performs at New York City's Madison Square Garden. The movie was shot during his sold-out tour in 2012.

Tags: Demi Lovato 4th of july Fourth of July 2013