Avalanna's family gathered last year for a play wedding between Routh and Bieber at the Jimmy Fund Clinic, and then traveled with her to New York City in February to meet Bieber, who had learned of the girl's love for him. In June, Bieber brought Avalanna on stage at the Apollo Theater.
Wednesday afternoon Bieber tweeted: "just got the worst news ever. one of the greatest spirits i have ever known is gone. please pray for her family and for her," and then, "RIP Avalanna. i love you."
Bieber was "just a dream," Avalanna's mother, Aileen Routh told the Globe after the February visit.
"We were Bieber fans before, but there is now a whole new respect for this kid that did such a great job with her and was just so graceful in doing it," she said.