Dijana Milojković, Miss Earth Serbia 2014, used Question Sticker to connect with her 112,000 followers on Instagram.
The former model, 31, who is battling aggressive womb cancer, was stunned when a woman asked: "Why bother making yourself look pretty, combing your hair and putting on makeup, when you know you are dying?"
Dijana tried to turn it into a joke, saying: "Does it mean if I am going to die I should go out with messy hair?"
However, the troll sparked outrage among Dijana's followers, including her ex-boyfriend Stefan Karić. "And why are you breathing when you know you will die?" he asked mockingly.
Instagram user "ivangromovnik" slammed the message as "morbid and repulsive."
"How this beautiful girl attracts sick people to ask something like this. Thousand questions I would ask this beautiful lady that has something to say," said another fan, going by the name "Korisnik".
In October 2016, the model revealed her diagnosis online, posting a photo with Stefan Karić, both with their heads shaved, to raise awareness of the disease. Shortly after the publication, she made a runway appearance to raise money for Mario Jurisić, a Serbian cameraman diagnosed with skin cancer.