Carson Palmer is calling it a career.

“Over the years I’ve had teammates who decided to hang it up and I would ask them how they knew when it was time to walk away. The answer was almost always the same: You just know,” Palmer wrote in an open letter to fans. “For me, that time is now. Why? Quite simply I just know.”

The 38-year-old Palmer is coming off a season that was cut short by a knee injury, and it’s no surprise that he thinks it’s time to move on. A three-time Pro Bowler, Palmer was a Heisman Trophy winner at USC and the first overall pick in the 2003 NFL draft.