"The world lost the most special boy and an absolute hero last night," Ben's dad wrote on social media.

He continued ... "Ben, you were the best son we could ever hope for, and you were my best bud ever. Your sisters were so lucky to have you as such a sweet brother."

"You fought so long and hard and beat so many odds," he added.

Ben -- who was diagnosed with glioblastoma (an aggressive type of cancer that can occur in the brain or spinal cord) about a year and a half ago -- got a chance to meet the Oilers team in March, even accompanying team captain Connor McDavid onto the ice before a game.

That night, Ben -- gearing up for another stint of chemotherapy -- wore a custom Oilers jersey with his last name "Stelter" and the number 2 ... as the fans and players provided support and words of encouragement.

Ben attended many Oilers games throughout the season ... and became a good luck charm for the team, evidenced by their impressive record with him in attendance.

"Ben’s coming to the game tonight and has his eye on the cup," Mike wrote in June. "The @EdmontonOilers are 10-0 with Ben in the building at Rogers Place. #LetsGoOilers #BenOilersStrong."

The organization addressed Ben's passing online, Tweeting ... "We are mourning the passing of our dear friend, number one #Oilers fan, good luck charm & inspiration, Ben Stelter. Although small in stature, Ben's impact on our team & community were massive.  Play La Bamba, baby. 💙🧡"

The Oilers were eliminated from the playoffs by the Avalanche in game 4 of the WCF. Colorado went on to win the Stanley Cup.

Ben's presence will forever be missed on the ice and in the locker room going forward.