Inter Milan have signed Belgium striker Romelu Lukaku from Manchester United for a club record fee of 80m euros (£74m) on a five-year deal.
Lukaku, 26, scored 42 goals in 96 games for United but leaves just two years after his £75m move from Everton.
He becomes the third most expensive signing by a Serie A club after the Juventus duo of Cristiano Ronaldo (£99.2m) and Gonzalo Higuain (£75.3m).
"Inter were the only club I wanted," said Lukaku.
"I'm here to bring the Nerazzurri back to the top."
In a statement, Manchester United said: "Everybody would like to thank Romelu for his efforts at the club and pass on our best wishes for the future."
Lukaku scored 15 goals in 45 games for United last season but was often overlooked in favour of England striker Marcus Rashford by manager Ole Gunnar Solskjaer.
He did not feature in any of United's pre-season games, with Solskjaer saying the player had an ankle injury.
Belgium manager Roberto Martinez said earlier this summer Lukaku "had to leave" the Premier League club, with Inter boss Antonio Conte indicating the ex-Blues striker was his top transfer priority.
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Lukaku's United career
Lukaku moved to United from Everton in 2017 and at the time was only the fourth player to score 80 goals in the Premier League before turning 24 - after Michael Owen, Robbie Fowler and Wayne Rooney.
In his debut season, the Belgian became one of only 11 United players to score 25 goals or more in a campaign since 1992-93. Cantona, Andy Cole and current United manager Ole Gunnar Solskjaer (25 each) are among the strikers who never matched Lukaku's 27-goal tally in a United campaign.
However, 26% of his United goals - 11 out of 42 - came in the first two months of his Old Trafford career.
Lukaku's departure leaves United with just three established forwards - Rashford, Anthony Martial and Alexis Sanchez - in addition to youngsters Angel Gomes, Mason Greenwood and Tahith Chong.
United have spent £140m this summer on Harry Maguire, Aaron Wan-Bissaka and Daniel James.
Analysis - Lukaku gone but United light in midfield
BBC Sport's Simon Stone on BBC Radio 5 Live:
Manchester United ended up in a very difficult position with Lukaku.
It goes back to last season when Lukaku did not feel he was being picked often enough by Ole Gunnar Solskjaer because of the style of play. During pre-season, when everyone thought the focus was going to be on Paul Pogba and whether he would turn up, Lukaku's attitude looked poor and he did not train. The one session he did train before the Leeds game, he told someone he felt a twinge and was not seen again.
In another session he watched on as his team-mates trained for 40 minutes - I had never seen anything like it. You knew there was no way back, he did not want to be there and Solskjaer did not want him there. In the end, Inter Milan came up with the money.
I knew Lukaku was going but I never felt they would get another forward in. Inside the club, the way Solskjaer wants to play, they have the forwards they need - Anthony Martial, Marcus Rashford, Alexis Sanchez and young Mason Greenwood. They only play one centre-forward and the rest are advanced midfield players like Jesse Lingard.
Where United needed someone was in central midfield. If you have an anchor, then Pogba can go forward more. He has knuckled down and responded. He might want to go to Real Madrid but has not created a situation like Lukaku did.
United let Marouane Fellaini and Ander Herrera go from midfield and now you are look at who is in the middle. If you take Pogba out, you have Scott McTominay and Nemanja Matic, that is not great.
They are in a difficult situation, do they massively overpay for players like they did with Sanchez or do they try to sell players to create space in their squad? They are in a position where they now have seven centre-halves.
The fans were saying, Bruno Fernandes, Bruno Fernandes, but people at United said they were never seriously in for him.