The family of Avalanna Routh (rooth) — who called herself Mrs. Bieber — said on their Twitter account that she died Wednesday.
Her pretend wedding to Bieber led to a social media campaign to help her meet the singer.
Bieber later arranged for girl to meet him in New York. He tweeted that the experience was inspiring and called it the best thing he’s done.
Routh suffered from an atypical teratoid rhabdoid tumor. Only 30 new cases are diagnosed in the U.S. each year.
The Dana-Farber Cancer Institute says Routh raised awareness about the disease and the need for greater research.