It was a father's final act of kindness for his beloved daughter, and it came to her five years after his death.
Bailey Sellers' father passed away from cancer when she was 16 years old.
Every birthday since then, the Tennessee college student has received a bouquet of flowers from her dad, which she says he pre-paid in advance so she would always have something from him.
In a heartbreaking post on Twitter last Friday, Sellers posted a picture of the final bunch of flowers she would be getting from her late dad.
"This is my 21st birthday flowers and the last. Miss you so much daddy," she wrote.
Along with the flowers, a final birthday card was delivered:
"Bailey, This is my last love letter to you until we meet again. I do not want you to shed another tear for me my baby girl for I am in a better place," he wrote.
"It is your 21st birthday and I want you to always respect your momma and stay true to yourself. Be happy and live life to the fullest. I will still be with you through every milestone, just look around and there I will be."
The card, featuring a trio of delicate butterflies, signed off: "I love you boo boo and happy birthday!!! Daddy".
The incredible story has touched hundreds of thousands of people, with the post getting more than 1.5 million likes on Twitter and thousands of retweets and well-wishes.