a 6-year-old girl with cancer

He called her “Mrs. Bieber” – making her the object of envy of girls all over the world.

Avalanna Routh, a six-year-old Bieber devotee—she claims she's been a fan for an incredible 80 years—who is battling a rare form of cancer called atypical teratoid rhabdotumor (or AT/RT), had the Valentine's Day date of a lifetime this year.

Last year, hospital staff arranged for young Routh to marry her crush in a ceremony that included flowers, cake, music and a cardboard cutout of Bieber. Shortly afterward, a Facebook campaign was launched “to help the little girl meet her 'Mr.'”

When Justin Bieber heard her story, he flew her and her family from Massachusetts to Manhattan to spend the day with him.

“I have Bieber fever,” the little girl told NBC News.

The low-key “couple” played Candyland, nibbled on Sour Patch Kids and cupcakes, signed each other’s autographs, and then Routh played with the pop star’s iconic hairstyle.

“It's been great… He wants to be my husband,” Routh told CNN.

Maybe Selena Gomez should watch out? (I'm kidding, Bieber fans. I'm kidding.)

“This was one of the best things I've ever done,” Bieber tweeted that day. “She was AMAZING. I'm feeling really inspired right now.”

“This is a beautiful story,” Aileen, Routh's mother, told CNN, “and we need to keep the momentum going and provide financial support to the search for a cure for AT/RT.”

The disease usually leads to death within nine months, but Routh fought against all adversities for five and a half years “with grace and humor” against the “very aggressive, rare disease.”