Lukaku did not always agree with the decisions being taken with his best interests in mind, but did enough to convince Mourinho that he was worth £75 million ($91m) when moving to Old Trafford in 2017.
A return to west London was on the cards that summer before the Red Devils swooped in, with Lukaku telling the LightHarted podcast: “I was gone, I was going to Chelsea.
“I was looking for an apartment, an apartment for my mum to stay in close to the practice facility, so I don't have to drive too far. And then Man U came.
“At Man U everybody was... I felt the trust more, where everybody wanted me to be there and that's the true story.
“People say 'Yeah, my agent [Mino Raiola]' and stuff like that - my former agent at the time - he did his job, he got the best opportunity for me, but the people wanted me the most and that was Man U. Everybody was wanting me. There was no doubting.
“They came and they told me - I was in New York - I get a phone call from this number and I'm like, 'Who's this?' Pick up, Jose Mourinho. 'Rom, how are you doing?' I'm like, 'Yeah, what's up, boss?'
“'I'm gonna get you back, we're gonna pay £75m plus £15m in bonuses by next week, so I expect you in LA. So go and do your s*** in LA and I'll see you after [in pre-season]'. I felt the dude was lying, like 'I'll see you'.
“Then the next thing I know, I wake up and had to go back to Everton on the July 7 and July 6, I wake up in the morning and I see they've agreed the deal, so I'm like, 'Man! They came in hard!'”
A move to Manchester saw Lukaku reunited with a coach who had previously overlooked him.
The 26-year-old was, however, to become a leading man for Mourinho during his time at United.
The pair were to endure the odd difference of opinion at times – with the Red Devils disappointed to see a star frontman rule himself out of contention for a starting berth in the 2018 FA Cup final – but a positive working relationship was enjoyed on the whole.
Lukaku added on linking back up with Mourinho: “When [I was at United], I remember we were in Moscow two years ago, we played CSKA, I told him, “Yo man, I wanted to kill your arse so bad” and we laughed about it.
“Me and Jose our relationship is… everybody has their own personal relationship with him, but me and him we bump heads.
“We bump heads, but I love him as a man. I think he loves me as a man, but we bump heads all the time. All the time. He might be picking on me, but then I’ll be picking on him. But he’s my guy, for sure, he’s my guy.”
Both Lukaku and Mourinho have now severed ties with United, with the latter still looking for work after being sacked in December 2018 while the former has signed for Serie A giants Inter.