Heartbroken Justin Bieber honored 6-year-old superfan Avalanna Routh, aka Mrs. Bieber, during his Sept. 29 concert, showing his fans just how much he truly cared about the young cancer patient.

Bieber paid tribute to the late Boston-area fan with a beautiful photo montage that was displayed as he sang 'One Less Lonely Girl' in Glendale, Ariz. Routh suffered from an atypical teratoid rhabdoid tumor that ultimately took her life on Sept. 26.

"Justin dedicated 'One Less Lonely Girl' to Avalanna [on Sept. 29]," Bieber's musical director and guitarist Dan Kanter told Hollywood Life. "There was a touching picture montage during the song and instead of choosing a 'lonely girl' as he usual does. Justin placed flowers on a empty seat. It was very emotional for all of us. She was precious."

The Canadian singer was notably affected by the news of Routh's passing, which he tweeted about to his 28 million followers as soon as he heard. "Just got the worst news ever," he wrote. "One of the greatest spirits I have ever known is gone. please pray for her family and for her."

Earlier this year, Bieber flew Routh and her family to New York City to have a Valentine's Day date, which "really inspired" the star. Since her passing, the Dana-Farber Cancer Institute has praised Routh for raising awareness about the rare form of brain cancer and need for more research.