Justin Bieber took to Twitter today to mourn the passing of 6-year-old Avalanna Routh, the feisty Merrimac girl with a rare brain cancer who won his heart last February. The pop star, who played CandyLand, ate cupcakes and talked music with the little Jimmy Fund lady in his Big Apple hotel suite around Valentine’s Day, 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.”