The 24-year-old is set to swap Goodison Park for Old Trafford after United finally agreed a fee with Everton that could top £100million with add-ons and bonuses.
The move, which will net the Belgian international upwards of £200,000 per week, is yet to be officially confirmed but Lukaku shared the details of his medical, which he undertook in California before being joined by his new teammates later today, with his 600,000 Instagram followers claiming it was "finito".
And speaking for the first time about the impending move he could scarcely be happier claiming it was the sort of opportunity that was too good to turn down.
"It's the biggest club in the world," he told ESPN. "It's a club that's hungry to win the league again, to be dominant in the world again. This is the sort of opportunity that I always wanted since I was a child and when they came calling I didn't have to think twice."
United have yet to make any official announcement and are flying to the United States on Sunday to begin an 18-day stay which will include friendlies with MLS sides the Los Angeles Galaxy and Real Salt Lake, plus matches against Manchester City, Barcelona and Real Madrid in the International Champions Cup.
Mourinho has prioritised the addition of a No.9 this summer following the injury to and subsequent release of Zlatan Ibrahimovic with Atletico Madrid's Antoine Griezmann, Andrea Belotti of Torino and Real Madrid's Alvaro Morata on his shortlist.
But he has instead opted for Lukaku, a player who has scored 20-plus goals in each of the past three seasons for Everton, with the man himself over the moon.
"I'm really delighted to hopefully be part of their history," he added. "Who would say no to the biggest club in the world? The best stadium in England, the best fans, it's the perfect opportunity.
"I always said that I wanted to play for a team that was challenging for every trophy that there is, and I think Manchester United at the minute wants to be that dominant team, that dominant force.
"And if you look at their history it says enough and to become part of a club like them is something that I really wanted, and I'm thankful for the opportunity that they gave me."
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