American singer Christina Grimmie shot dead outside concert. Twitter reactions

In another tragic case of gun violence in the United States, 22-year-old American singer Christina Grimmie was shot dead at her concert venue in Orlando, Florida just as she was signing autographs for her fans. Grimmie's killer shot himself after the incident.

A former contestant of the reality show The Voice, Grimmie was performing with the band Before You Exit late Friday. The young singer had only recently signed an album deal.

Only 12 hours ago, Grimmie had tweeted a vine inviting fans to the concert:

Shocked fans took to social media to remember the young singer:

Two weeks ago, a gunman shot dead two people in NYC, where hip-hop artist TI was set to perform. Meanwhile, Grimmie's death remains a mystery.