Harrison, 38, posted an Instagram photo of him walking out of the Steelers' tunnel with the words "I'M BACK" in bold, along with a message that "like a fine wine" he was "getting better with age."
Shortly after that, the Steelers' official Twitter account tweeted Harrison's image while commenting, "What he said."
Harrison wanted to undertake a rigorous six-to-eight-week training schedule to ensure he was up for another year in pads. He highlighted those workouts daily on social media, often lifting absurd amounts of weight. Apparently, he has completed that training.
Harrison's agent, Bill Parise, told ESPN in late February that Harrison planned to honor his contract, which has one year remaining. The Steelers were bracing for his return.
"He's working out awfully hard for a retired guy," said coach Mike Tomlin on Saturday night after the draft.