(Family Photo)

Seven-year-old Millie Flamm got the surprise of her life Saturday evening when singer Justin Bieber walked into her room at Primary Children's Medical Center in Salt Lake City and delivered a private concert.

Bieber had a performance scheduled at Salt Lake's Energy Solutions Arena, and Flamm had had tickets for weeks.

But she developed a fever while undergoing treatment for leukemia, and her family was forced to sell them.

When Millie's family and friends heard the news, they took to the Internet and social media to share her story with Bieber, who apparently got the message.

"He came in and was so loving towards her and gave her all the attention," family friend Mary Ann Horne, who was in Millie's hospital room at the time of the visit, told ABC News. "The look on her face, I've never seen anything like that. I had to turn away because I started crying."

While surrounded by her family, Bieber held the young girl's hand.

He also played Millie's favorite song, "Baby," on his guitar. When the song ended, Bieber gave Millie a kiss on the cheek and handed her his guitar pick.

Horne said the visit changed Millie's world.

Following the kiss, Millie turned to her mother, Amanda Flamm, and said, "You are never going to wash my face again."

Horne said the meeting was a huge boost to Millie and her whole family, giving everyone the motivation to continue.

"He was an incredible person," said Horne, "the way he just changed her world."

A source close to Bieber called the singer "extremely generous with his time," saying he "visits with many fans who are facing challenging situations. This is just one example, and it happened to take a little extra time."