Longtime Pittsburgh Steelers linebacker James Harrison officially announced his retirement from the NFL today after 15 seasons. 

Harrison, who will turn 40 next month, made the announcement on Instagram this morning with a post that featured pictures of his kids and a caption that reads, "I've missed way too much for way too long," Harrison wrote. "I'm done. Many thanks to my family, coaches, the fans, and everyone who played a role in my football life."

Harrison had previously told ESPN: "I told my son [James III] he could play contact football when I stop, so I'm going to have to give it up in the near future, so he can start getting adjusted to playing. I don't want him to wait too long."

After playing his college ball at Kent State, Harrison went undrafted in 2002, as most teams in the NFL deemed him too small to be an effective pass rusher. As a result, Harrison played for NFL Europe's Rhein Fire in 2003 before joining the Steelers in 2004. He remained with the team for nine seasons, which included five Pro-Bowl appearances, two First-Team All-Pro selections, and the NFL Defensive Player of the Year award in 2008. 

Harrison spent a season with the Cincinnati Bengals in 2013, but returned to Pittsburgh the following season and ultimately ended his career in New England after being released by the Steelers last season. After having played just 40 snaps over 14 games with the Steelers in the 2017 season, Harrison was on the field for 69 snaps with the Pats in Super Bowl LII.

He ranks as the Steelers' all-time sack leader with 80.5.