He was just five years old.

The team posted a touching message in the Bullmastiff's honor minutes ago ... saying, "We are sad to announce the passing of our beloved mascot, SJ. We are so grateful for his many years of loyal support and cherish all of the wonderful memories he helped create for fans young and old."

SJ was the son of the Browns' first live mascot, Swagger ... who held the position from 2014-19. Swagger passed away in 2020 after a battle with cancer.

SJ handled gameday duties until his passing. Details surrounding his death were not released.

The team has not announced whether it plans to keep the recent tradition alive and enlist another dog for the job ... or if it will choose to discontinue it altogether.

SJ was introduced with a special video back in 2019 ... showing him roaming around Cleveland Browns Stadium as the "Rocky" theme played in the background.