Justin Bieber mourns fan Avalanna Routh who lost battle to cancer

justin-bieber-avalanna-routh.jpgEarly this year, Justin Bieber found out about a family's Facebook campaign to get their six-year-old cancer-stricken daughter, Avalanna Routh, to meet her favorite popstar. Touched, Bieber arranged to fly Avalanna -- who called herself "Mrs. Bieber" -- to fly to New York to visit him with "Today" show cameras on hand.

"Hangin' out with a special little girl. #MrsBieber," he tweeted of his friend, who was stricken with aggressive atypical teratoid rhabdoid tumor cnacer. "That was one of the best things i have ever done. She was AWESOME! Feeling really inspired now! #MrsBieber."

They remained friends, as he often used Skype and Facetime to catch up with his little pal. He also invited her to join him as he made promo rounds for his new "Believe" album, and she joined him on stage at the Apollo Theater.

Today, Bieber learned of Avalanna's passing. "just got the worst news ever. one of the greatest spirits i have ever known is gone," he tweeted as "RIP Avalanna" began to trend on the social network. "please pray for her family and for her. RIP Avalanna. i love you."

Avalanna was also mentioned by Jessica Biel during the "Stand Up to Cancer" telethon recently.

Visit NBCNews.com for breaking news, world news, and news about the economy

Photo/Video credit: NBC