Steward wrote an emotional remembrance of his fiancee on Instagram next to a smiling picture of Burns.
"You have the biggest heart I have ever seen in my entire life and I promise you that it will live on in me, our family and every single soul you have touched," Steward wrote online. "We will all honor everything you stand for in life. I will continue to be the person that you always bring out in me. Believe me when I say that I deeply love you with every ounce of everything in me."
Burns was reportedly diagnosed with a "rare ovarian cancer" in December, according to the charity campaign page she posted. She and Steward had been fundraising for their charity campaign "Fight Like a Girl."
The couple were engaged just seven weeks ago after more than three years of dating. The couple met when they were students at Clemson University.
The Buffalo Bills team issued a statement confirming Burns' death alongside a picture of the smiling couple.
“From the day Brittany arrived in Buffalo with Tony, she was an active member in the community through the Buffalo Bills Women’s Association," team officials said in a statement. "Our prayers and heartfelt condolences go out to Tony Steward and the family of Brittany Burns during this most difficult time.”