The fan, Delaney Clements, posted a photo of their meeting on Instagram and detailed how it all happened.
"I was just laying down taking a nap in my room when my mom said I had a visitor. And I thought it might just be another person coming to see how I was," she wrote. "Then suddenly the most amazing miracle happens...Taylor Swift walked into my bedroom and spent the afternoon with me just talking and hanging!!!! I am beyond Blessed for everyone's help and support!!!"
Swift also posted some pics of her own from the time they shared, writing, "Merry Christmas Baby."
Clements has been battling neuroblastoma since 2010. Thousands shared the #DelaneyMeetTaylor hashtag on Twitter in an effort to catch the pop star's attention.