BOSTON (WHDH) -- The young girl who stole the hearts of many, including pop star Justin Bieber, passed away Wednesday morning.

Avalanna Routh, known as Mrs. Bieber, lost her hard-fought battle with ATRT, a rare form of brain cancer.

“Even though we knew how sick Avalanna was, you’re just never ever ready to hear that kind of news in the morning, especially,” said Sharon Wimmer, a family friend.

The 6-year-old was known as a girl who truly loved everyone. The news of her death was announced via Twitter Wednesday morning: "Our darling Avalanna went to Heaven this morning. Oh Avalanna, the brightest star - you took our hearts with you, our greatest Love."

Share your memories and condolences for Avalanna here.

In Avalanna’s hometown of Merrimac her story has touched everyone.

“We’re all just trying to pull it together for the family. They lost their daughter. We’re worried about how they’re going to function through this,” said Heather Lessard, who lives in Merrimac.

Avalanna, a huge fan of Justin Bieber, took on the nickname Mrs. Bieber after family and supporters staged a wedding. When the two met face-to-face, Avalanna’s story gained national attention.

Bieber shared his grief on Twitter: "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" and directly after he said, "RIP Avalanna. I love you."

Avalanna’s story was also profiled on a recent network television Stand up 2 Cancer special. It gave new focus to her rare form of cancer -- atypical teratoid rhabdoid tumors, also known as ATRT.

“The research in my lab is upon ATRT and indeed we’ve begun to identify targets and we’re hoping to open up our first clinical targeted trial, but it makes me so sad that we were not in time for Avalanna,” said one of Avalanna’s doctors.

Avalanna’s death is making people even more determined to help find a cure.

“I hope that someday in the future other people don’t have to go through this and everybody works to find some way to not let this happen to little children anymore,” said Wimmer.

The Dana Farber Cancer Institute also released a statement about Avalanna on Wednesday:

"We are saddened by the passing of Avalanna Routh. She was a very courageous young person who lived her life with grace and determination. By generously sharing her story, she raised awareness worldwide about atypical teratoid rhabdoid tumors and articulated the need for greater research of this rare cancer. Our thoughts are with her family."

Avalanna’s doctors said during the last few weeks she started to get really tired, but always had high spirits.