What started as one Illinois teenager's idea to set up an Instagram account to document his ailing great-grandmother's last days has turned into a social feed that has delighted and inspired thousands.

This image was posted to great-grandma Betty Simpson's Instagram account Jan. 26, 2014. grandmabetty33/Instagram

Zach Belden, 18, set up the Instagram account for his great-grandma Betty Simpson, 80, shortly after her cancer diagnosis as a way to celebrate her life and record her ongoing battle with the disease. Neither expected the account would amass a following of more than 20,000 and counting.

"He loves me so much, that's why he did it. He doesn't want to lose me and he's just good to me," Simpson said of her great-grandson. "I didn't even know he was doing this."

She told ABC News she has "been very sick," and almost died twice six months ago. Since then, Zach has been at her side (whenever he's not at school), documenting short snippets of his Simpson's everyday life in photos and short video clips and posting them to the photo-sharing site.

One of the most popular videos shows Simpson getting her groove on to Pharrell William's hit song "Happy."

"Everybody liked that," Simpson said. "I got calls from California and all different places. They said they thought that was very cute."

Another clip shows Simpson shimmying to some big band music.

Simpson says she is full of gratitude and love for all of her followers and feels like a celebrity each time she receives a new follower. "Wouldn't you?" She asked.

Her recent following even boasts a few celebrities, including Pharrell Williams, which Simpson thinks is just "lovely."

But the great-grandmother says she doesn't want to let her new social media status go to her head. Instead, she says, she plans to live out her days "just being with family" and "living minute to minute."

Follow Simpson's account here.