When Bailey Sellers turned 17 on Nov. 26, 2013, there was an unexpected bouquet of flowers waiting for her on the front porch.

“Happy birthday,’’ the note read. “You’ll receive these until you’re 21. Love, Dad.”

Her father, Michael Sellers, had died earlier that year from pancreatic cancer at 56. One of his last acts was setting up the recurring flower delivery, making each birthday another opportunity to hear from him anew.

Since that day, she had dreaded her 21st birthday, when she knew she’d hear from her father for the last time, she said in a phone interview on Monday. His final delivery came to her home in Johnson City, Tenn., on Friday, and her photo of her father’s note struck an emotional chord on social media, where it was shared hundreds of thousands of times.

“It means the world to me,” she said of her father’s final note. “I’m going to cherish that for the rest of my life.”

Ms. Sellers, a junior studying psychology at East Tennessee State University, is the youngest of four children. She was 16 in 2012 when her father slept through most of Christmas — his favorite holiday — and his family realized something was wrong. Doctors found tumors spread throughout his body and determined that he had Stage 4 pancreatic cancer.

In the middle of her sophomore year of high school, she decided to drop out so she could be home-schooled while caring for her father. She would get his medicine and cook for him while her mother, Kristi Sellers, was…

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