Challis died on Tuesday at his home in Freedom Township, Pa., a distant suburb of Pittsburgh. He is survived by his parents, Scott and Gina, and his sister, Lexie.
During Challis' visit with players, coaches and staff members back on June 25, the teenager formed friendships with numerous members of the organization. Saddened by Tuesday's news, a number of those individuals reacted to Challis' death.
"John had every reason to complain about his situation, but he chose not to," president Frank Coonelly said in a released statement. "What he did do was show unfathomable courage and great wisdom for someone so young. John's body could not win the battle with cancer, but John's tremendous spirit will live on amongst all those he and his story impacted across the country."
For LaRoche, the news was taken especially hard. He had befriended Challis after meeting him in June and stayed in contact with the youngster during the summer. Bonded by their love for deer hunting, the two had planned to spend time hunting together at LaRoche's ranch in Kansas over the winter.
"I knew that the chances weren't real good that he would be around for it, but I was hoping he would make it," LaRoche said. "God had another plan for him."
LaRoche last talked to Challis about three weeks ago, calling his family's home after learning that doctors had given Challis only a few more weeks to live.
"It's depressing," LaRoche said. "It makes you realize how short life is and how unfair it can be. You sit back and you look at a guy like that who knows his days are numbered, and never got to play in the big leagues and got one high school at-bat and was still loving life. ... He was special to me."
Back on that June day, Challis wrote a message on the white board of the Pirates clubhouse that read: "Have fun, [it's] the reason why we play ball." Those words have since been erased. However, it's obvious they have not -- and will not -- soon be forgotten.
"What he brought [the team] for the day he was with us, the courage that he showed, the message that he had, just the message that he sent and the number of lives that he touched was phenomenal," manager John Russell said. "I think if he was here today, he would say, 'Don't fret.' He was a great inspiration to everyone."