And with the Belgian now closing in on a £75 million switch to Old Trafford having successfully undergone a medical, the 24-year-old has revealed exactly why he wants to work under the United manager again.
He told ESPN : "[Mourinho is] a guy who I wanted to play for since I was 10 years old, so now to have the opportunity to work under him again is great. We've been in contact. He explained to me how the club was like, what he expects from me.
"You know, we were together under different circumstances. Obviously, the first time when I met him, I was still a young kid, and I was eager to play. And he understood my decision why I left at the time.
"I returned on the pitch. Now I'm 24. I'm a grown man. He sees the maturity that has grown throughout the years, so I'm really thankful for the opportunity he gave me again."
Lukaku went on to describe his impending move to United as "the perfect opportunity" and that Mourinho is the right manager to help him achieve his goals.
He added: "I think he wants to improve me, make me a better player than I am today, which is good. I always want to improve. I always want to work on the good stuff, but also the bad stuff.
"He knows how to make players better, and make players winners as well. For me, I think it's the perfect opportunity.
"I'm 24. I never won a major trophy, but I'm eager to win something and to be part of a team that wins trophies, and I think he's the right guy to help me in that."