Flavious was killed in action in the opening attack of the Battle of St. Quentin Canal, when the Allies assaulted the fortified Hindenberg Line. His sister Josephine Merrow received the following letter written 25 October 1918 from Flavious's commanding officer, Captain Edgar H. Bain:
Dear Miss Merrow,
By this time, I haven’t any doubt but that you have heard of your brother’s heroic death. He was killed in action, September 29, 1918 at the battle of Bellicourt, when the 30th Division stormed and took the Hindenburg Line. He was a machine gunner and died fighting. I loved your brother and his death was a blow to me. I was not in the battle, as I was not with my Company at the time. But he did himself honor.
I sympathize with you good people, his sister and poor old mother. So many of us will pay the penalty of war before it is won.
I am here now only by the grace of God, as it does not seem possible that I could get through.
Assuring you of my deepest sympathy in your bereavement, I am
Edgar H. Bain
Flavious is buried (Plot A, Row 15, Grave 1) in the Somme American Cemetery in Bony, France.