Justin Bieber fans have taken to the Internet to pay their respects to Merrimac’s Avalanna Routh — known to her family and friends as “Mrs. Bieber” — who died Wednesday after a long battle with an aggressive form of brain cancer. Routh became a celebrity after her very public crush on singer Bieber culminated with a visit from the singer in February. After hearing that Routh, 6, had passed, Bieber tweeted to his followers: “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.” He added in separate tweets: “RIP Avalanna. i love you,” and “please show respect to her and her family. say a prayer for her and for them. i miss her.” Bieber also dispatched a link to the website for Cure ATRT, a group that helps people dealing with Routh’s specific diagnosis (atypical teratoid rhabdoid tumor). The news of Routh’s death was verified by her family, also via Twitter, who announced to her 150,000 followers: “Our darling Avalanna went to Heaven this morning. Oh Avalanna, the brightest star — you took our hearts with you ...” It seems that Routh’s last post was on Sept. 13. She tweeted: “Trying to stay up late to see my husband on Americas Got Talent #supportingmyman #mrsbieber.” She had also sent a thank you note to Jessica Biel for participating in Stand Up To Cancer.