Justin Bieber's biggest fan Avalanna Routh, aka "Mrs. Justin Bieber," died from brain cancer this week. The 6-year-old girl's parents announced the tragic news via Twitter, "Our darling Avalanna went to Heaven this morning. Oh Avalanna, the brightest star - you took our hearts with you, our greatest Love;(."Avalanna gained worldwide recognition when the teen heartthrob learned about a Facebook campaign created to help the ailing child meet him. Upon finding the page, which had 12,000 followers at the time, the 18-year-old pop singer retweeted the campaign to his fans, and then made the ultimate gesture of love -- he flew Avalanna and her family to Manhattan to celebrate Valentine's Day with him. Avalanna and Bieber spent the day playing games, cuddling and hanging out together. Pictures of the two show a glowing Avalanna overjoyed with her idol. And Bieber himself was absolutely smitten with Avalanna. Following their incredible meeting, he Tweeted, "That was one of the best things I have ever done. she was AWESOME. Feeling really inspired right now! #MrsBieber. " He also posted a picture of them together. Bieber was devastated to learn about Avalanna's death Wednesday. He 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. RIP Avalanna. i love you. please show respect to her and her family. say a prayer for her and for them. i miss her." Up until her death, Avalanna remained a devoted Belieber. Just two weeks ago, she Tweeted, "@justinbieber Trying to stay up late to see my husband on Americas Got Talent #supportingmyman #mrsbieber." Avalanna battled atypical teratoid rhabdoid tumor, or AT/RT, for five and a half years. The rare condition afflicts only 30 people a year.