Under Armour has secured one of its biggest stars.

Philadelphia Phillies slugger Bryce Harper has re-signed with the Baltimore-based apparel maker, he announced on Instagram on Tuesday.

Harper, whose partnership with Under Armour began 15 years ago, signed a new six-year agreement, according to a source with direct knowledge of the negotiations who spoke on condition of anonymity.

Harper’s previous deal with Under Armour recently lapsed, and in the comment section of a TikTok video last week, Harper said he was a “Free agent in the apparel/footwear category right now” when asked about his Nike shoes. But a source said Harper was in the process of negotiating a new deal and hadn’t ruled out a return to Under Armour.

Harper’s return is significant for Under Armour, which lost Golden State Warriors guard Stephen Curry about two months ago. Curry and Under Armour had partnered for 12 years. The company has added new talent, though, such as Colorado Avalanche defender Cale Makar.

Harper, 33, remains the crown jewel of Under Armour’s catalog. He’ll remain front and center as he plays for the United States in the World Baseball Classic this spring.

Their relationship is long-standing; Harper signed with Under Armour when he was 17.

“They wanted me from the jump,” Harper said in an Under Armour-sponsored interview with Boardroom in September. Harper was still trying to make a name for himself when the brand began pursuing him. “For Under Armour to kind of give me that opportunity was huge,” he said.

The Washington Nationals selected Harper with the first overall pick in the 2010 draft, and he has since earned two MVP awards and eight All-Star nominations. When Harper re-signed with Under Armour in 2016, the 10-year extension was the largest endorsement deal in history for a baseball player, according to ESPN.

Kevin Plank, the CEO and founder of Under Armour, has been trying to salvage the brand amid sales and revenue declines. Under Armour’s stock value, which decreased in recent years, has jumped more than 25% over the past few weeks following a huge stock buy from Prem Watsa, a Canadian billionaire.

Plank, meanwhile, recently stepped away from further development projects at Baltimore Peninsula and approached Maryland state officials about purchasing his historic horse farm. He sold the Sagamore Pendry hotel in September, too.