Harrell had been thinking long and hard about his future - return to U of L for his junior season or turn pro and enter the NBA Draft.
"Honestly, I didn't go back and forth," Harrell said. "I didn't know what I wanted to do."
But after a long chat with his parents on Sunday night and a conversation early Monday with U of L coach Rick Pitino, Harrell said he was finally "set" on what he wanted to do.
So, Harrell called his parents and informed them of his final decision and then made a Tweet that sent CardNation into a tizzy.
The 6-foot-8 Harrell announced he was returning to school for his junior season, giving the U of L interior game a major boost.
"I've written so many pros and cons, it's not even funny," Harrell said. "By coming back, I feel like I can improve a lot of things.
"I feel good about my decision. It's the best decision for me, to come back and get better."
U of L coach Rick Pitino, who is out of town, called it "obviously great news," while teammate Wayne Blackshear said Harrell "made a good decision," because he "can only get better."
Harrell improved a ton during his sophomore season, recording 11 of his 12 double-doubles in the final 22 games of the season. He averaged 14 points and 8.4 rebounds a game and was named American Athletic Conference Most Improved Player and was also tabbed to the AAC first team.
While he said NBA folks told him he would be picked between No. 17 and 30 in the Draft, Harrell said they told him he was "raw" offensively and could make strides in that area.
"They liked my energy and passion," he said.
Harrell said he can get his ballhandling better and more consistent on his 15-foot jumper, noting he and Pitino have talked about "extending his range" beyond the three-point line.
"I feel like when I add those things I am going to be a better player and also going to make my team better," he said. "They felt like defensively I was pretty good but that I was kind of raw on offense."
Harrell was named co-captain along with Wayne Blackshear and said he's not going to "sugar coat" anything for his teammates. He said he will try to be the best leader possible.
"I feel like with the team we have, everybody just has to work," Harrell said. "We had a great run this season. No telling what we can do next season with the guys getting to work."
"I'm ready to get back into the gym with my team and with my coach," Harrell said. "I'm ready to get back to work and improve.
"I feel like this decision is right. I know a lot of guys are stressed out about a decision like this, but I think it will all work out for the best for me. Nothing is going to change for me, my work ethic is not going to change. I'm going to keep working towards where I want to go."