Justin Bieber Credit: Instagram

Justin Bieber delayed the start of his concert in Salt Lake City, Utah, Jan. 5 -- but it had nothing to do with his recent marijuana controversy.

The 18-year-old singer paid a special visit to leukemia patient Millie Flamm at Primary Children's Medical Center, as the 7-year-old was too sick to attend the show. "He was so sweet to her," the girl's mother, Amanda Flamm, told Deseret News. "He walked in and her whole face just lit up."

Bieber performed a song while holding Mille's hand and gave her his guitar pick. "She is squeezing on to it with all her might and will not let it go," Amanda said.

Before he left, the "Beauty and a Beat" singer gave his fan a kiss on the cheek. "You are never going to wash my face again," Amanda quoted her daughter as saying.

The Canadian crooner shared a picture of his visit via his Instagram account. "Look at this bundle of joy," he wrote in the caption. "I love her."

According to Amanda, Bieber's visit "has re-energized all of us" as Millie continues treatment. (She was first diagnosed with leukemia three years ago and relapsed two weeks ago.)

Said Amanda, "We are ready to keep going and fight harder with all this backing and this fun thing that has happened, and keep going and keep fighting."

It was a sweet gesture from Bieber, who's been making headlines since TMZ published pictures of the musician smoking what appeared to be marijuana in a California hotel room Jan. 4. Though the singer has yet to address the incident directly, he tweeted about "growing and learning" and "trying to be better."

Behind the scenes, however, a source told Us Weekly Bieber's team "isn't happy about those photos. They are grilling security about who could have taken them."