Justin Bieber performs to Avalanna Routh at the Apollo Theater in New York City. Credit: Will Hart/NBC/NBCU Photo Bank

"Mrs. Bieber" has passed away.

Avalanna Routh, a six-year-old cancer patient who Justin Bieber "married" on this past Valentine's Day, has died from a rare form of brain cancer.

"Our darling Avalanna went to Heaven this morning." her parents tweeted on her account Wednesday. "Oh Avalanna, the brightest star -- you took our hearts with you, our greatest Love."

Routh became known as "Mrs. Justin Bieber" after the 18-year-old "Boyfriend" singer surprised his young fan with a Valentine's Day date in NYC. The Boston-native and her family played board games, ate cupcakes and threw a pretend wedding with Bieber.

"That was one of the best things I have ever done. She was awesome!" Bieber tweeted after their meeting. "Feeling really inspired now! Mrs. Bieber."

And their friendship continued past their first visit. The two reunited in June for an interview on the TODAY show. On Sept. 13, Routh tweeted, Justin Bieber, trying to stay up late to see my husband on Americas Got Talent. Supporting my man. Mrs. Bieber."

Bieber has not yet commented on Routh's death, but he previously shared a touching video of their first meeting titled, "Me and Mrs. Bieber."