The Phillies star right fielder was spotted sporting a Phillie Phanatic headband during Thursday's game.
He even posted a picture of himself wearing it on Instagram, simply saying "SO Phanatical."
The Phillies Twitter account also took notice.
Fans on social media responded trying to figure out where to get one.
The team tweeted back anyone who asked saying the headbands are sold at the New Era Phillies Team Store at Citizens Bank Park.
This was not the first time Harper donned Phanatic-inspired clothing.
On Opening Day, Harper wore Phanatic cleats.
On his footwear decision, Harper told reporters at that time, "Just bring some fun to the game. The Phillie Phanatic's always happy and smiling, so why not?"
A few weeks later, he gifted the Phanatic a much larger version of the cleats for the mascot's birthday.