Grundy informed Scout.com that following his senior season he will do a post-graduate year at Hargrave and become a member of the 2015 recruiting class.
"I want to be an impact player from day one at the college level," Grundy told Scout.com.
"Coming back and playing for coach [A.W.] Hamilton will not only get me ready on the court but also off the court. I want to continue to develop my skill set so I can play the three in college."
Hamilton said Grundy has shown improvement on the court since transferring from Lexington (Ky.) Henry Clay during the offseason.
"Trey's grown so much as a player and a person since arriving to Hargrave," Hamilton said. "He's got a chance to be a big time player and play at a high level. I'm very excited about having him come back next year."
Among the schools currently showing interest in Grundy are Old Dominion, Appalachian State, East Tennessee State and Duquesne.
Grundy, a 6-foot-6 forward, is currently regarded as a three-star prospect on Scout.com.