Justin Bieber tweets about the death of a 6-year-old fan known as Mrs. Bieber

Justin Bieber is heartbroken today after one of his youngest fans, 6-year-old Avalanna Routh — better known as Mrs. Bieber — died of cancer. The “Boyfriend” singer tweeted a sweet message about the Boston girl on Wednesday afternoon, writing, “Just got the worst news ever. One of the best spirits I've ever known is gone. Please pray for her family and for her. RIP Avalanna. I love you.” About an hour later, he wrote, “Please show respect to her and her family. Pray for her and for her. I miss her.”

Routh gained national attention last year when she pretended to marry Bieber in a wedding ceremony staged by the doctors and nurses at the Boston hospital where she was being treated. The day before Valentine's Day, the singer personally flew her and her parents to New York to meet him, where they spent an afternoon playing board games and just hanging out. The Bieber even let the cutie play with his famous hair! At the time, he tweeted: “It was one of the best things I've ever done.he was AWESOME! Feeling really inspired now!” and used the hashtag Mrs. Bieber. Routh performed with Bieber at the Apollo Theater and when he appeared on “Today” in June, he said the two continued to stay in touch via iChat and FaceTime.

Unfortunately, Routh was ill for most of her life. Dr. Charles Robert of the Dana-Farber Cancer Institute, where Routh was treated, told the Associated Press that she was diagnosed with a rare teratoid rhabdoid tumor when she was just 18 months old – only about 30 of these cases are diagnosed each year in the U.S. She “responded to initial treatment for quite a while, but the cancer kept coming back and eventually she stopped responding” and died at her home in Merrimac, Massachusetts, Robert said. The Dana-Farber Cancer Institute issued a statement on Routh's death, saying, “She was a very brave young person who lived her life with grace and determination. By generously sharing her story, she raised awareness of atypical teratoid rhabdoid tumors around the world and highlighted the importance of increased research into this rare cancer.”

Routh's family also posted a beautiful farewell message on Twitter. “Our beloved Avalanna has gone to heaven this morning,” they wrote. “Oh Avalanna, the brightest star – you took our hearts with you, our greatest love.”

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