Sixteen-year-old Georgia lives in New Zealand, and in 2014 she was diagnosed with acute myeloid leukemia. She's also a massive 5 Seconds of Summer fan.
In the video, band members Luke, Michael, Calum, and Ashton told Georgia to "keep on keeping on".
They also told her they hope she'll be at their upcoming Sydney concert, adding that they have "lots of hugs" waiting for her.
Georgia told BuzzFeed that she started crying when she opened the video for the first time. "Honestly it just felt really nice to know that they actually kinda care about me."
At this stage, Georgia will have to wait and see if she will be in a well enough condition to attend 5SOS's Sydney concert, but really hopes she can make it.
"I was diagnosed in 2014 and had tickets to see them in 2015... they were my motivation to get better fast enough so I could go see them. They've done a lot for me."