Demi Lovato released a preview of her new song Heart To Heart on Wednesday.

"When your soul finds the soul it was waiting for. When someone walks into your heart through an open door. When your hand finds the hand it was meant to hold, don't let go," she sings on the slow tempo track. "Someone comes into your world, suddenly your world has changed forever."

The song will appear on the soundtrack of The Mortal Instruments: City Of Bones. Some of the other artists who will be featured on the movie's soundtrack include Zedd, Owl City, Jessie J, AFI, Youngblood Hawke and Colbie Caillat. See the full tracklist of the album, which will be released on Aug. 20, here.

The movie is set in New York City and is based on a book series written by Cassandra Clare. It follows the life of teenager named Clary Fray who finds out that she is a Shadowhunter - a half-angel warrior who has to protect Earth from demons. After her mother disappears, the young girl has to join other Shadowhunters. She is then introduced the Downworld, which has dangerous creatures.

Lily Collins plays the lead character Clary and her mother is played by Lena Headey. Other actors in the film include Jamie Campbell Bower, Jonathan Rhys Meyers and Kevin Zegers.

"I'm so excited! I had read and really loved the books," Collins told Glamour about starring in the film, cited in the magazine's June issue.

With the fan anticipation for the film mounting, Collins also said she doesn't want to let them down.

"The fans [in Toronto, during filming] were amazing. They'd bring us cookies, mugs, tea, drawings, everything. I want to make sure I live up to their expectations as Clary," she said.

The Mortal Instruments: City Of Bones comes to U.S. theaters on Aug. 20.

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