Manchester United have signed Alexis Sanchez from Arsenal, in a swap deal with midfielder Henrikh Mkhitaryan.
Chile forward Sanchez, 29, who almost joined Manchester City last summer, has signed a four-and-a-half-year deal worth £14m a year after tax.
City ended their interest last week as they felt making him their best-paid player may affect team spirit.
Mkhitaryan, 29, moves in the opposite direction to Sanchez after scoring 13 goals in 63 appearances for United.
The Armenia international moved to Old Trafford from Borussia Dortmund for £26.3m in July 2016.
He has made only 10 Premier League starts this season, and it is understood there was a breakdown in trust between him and United manager Jose Mourinho, which was reported by the BBC.
'Glory, Glory Man Utd' - how did it come to this?
United's signing of Sanchez, who will wear the number seven shirt, was announced on the club's Twitter account with him playing 'Glory, Glory Man Utd' on a piano.
He will be available for in the Red Devils' FA Cup fourth-round tie at Yeovil Town on Friday, which will be shown live on BBC One from 19:30 GMT.
And the League Two club tweeted a picture of their sparse-looking away dressing room with the message: "You said you've joined "the biggest club in the world" so it's only right you start your United career in the biggest away dressing room in League Two - *maybe."
Sanchez has scored 80 times for Arsenal since joining from Barcelona for £30m in July 2014, and was last season's top scorer with 30 goals in all competitions.
"I am thrilled to be joining the biggest club in the world," said Sanchez. "The chance to play in this historic stadium and to work with Jose Mourinho was something I could not turn down.
"I am very proud to be the first Chilean player ever to play for United's first team, and I hope I can show our fans all around the world why the club wanted to bring me here."
Sanchez almost teamed up at City with former Barcelona boss Pep Guardiola in a £60m move last summer, but his deadline-day transfer collapsed when Arsenal failed to sign Monaco midfielder Thomas Lemar.
Since that move did not materialise, Sanchez has had less of an impact, scoring 0.37 goals per game compared to 0.63 last season, with several pundits commenting on his on-field demeanour.
In a statement on Instagram, Sanchez said: "There are people [former club players] who have spoken with no knowledge of what happens inside the club and cause damage.
"I must say I always gave 100%, until the last day."
Arsenal manager Arsene Wenger denied there was a rift between the Chilean and his team-mates, but admitted the uncertainty over his future has affected team morale.
With Sanchez's contract at Arsenal due to expire at the end of the season - when he would be available on a free transfer - Mourinho has made him his first signing of the January transfer window.
The Portuguese said: "Alexis is one of the best attacking players in the world and he will complete our very young and talented group of attacking players.
"He will bring his ambition, drive and personality - qualities that make a Manchester United player."
Mkhitaryan ends underwhelming United spell
Mkhitaryan, who has scored once and contributed five assists in 15 Premier League appearances this season, joined United when Mourinho pipped Wenger to sign him.
His last appearance was in the FA Cup third-round win over Derby on 5 January, and he was left out of subsequent Premier League matches against Stoke and Burnley.
He will be available to play in Arsenal's Premier League game at Swansea on 30 January as he is cup-tied for the club's Carabao Cup semi-final second leg against Chelsea on Wednesday.
"I'm very happy that we could finish this deal," said Mkhitaryan. "It's a dream come true because I've always dreamed of playing for Arsenal. Now I'm here, I'll do my best for this club to create history."
Mkhitaryan did not start a Premier League game in almost three months after he was substituted at half-time during his full United debut against Manchester City.
Yet his form improved during the second half of last season and he scored as United beat Ajax in the Europa League final in Stockholm in May.
But, in November, Mourinho said Mkhitaryan's performances had been "decreasing step by step".
Before he moved to Old Trafford, the Armenia captain was the 2015-16 Bundesliga player of the season, and scored 23 goals in all competitions.
Wenger said: "Henrikh is a very complete player. He creates chances, he defends well, he can absorb distances and he's very committed as well. I must say he's a player who has all the attributes."
Sanchez & Mkhitaryan in numbers
- Since joining Arsenal in the summer of 2014, Sanchez has scored 60 goals and been involved in 85, more than any other Arsenal player in the Premier League. Only Romelu Lukaku, Sergio Aguero and Harry Kane have scored more.
- Only Mesut Ozil (378) has created more goalscoring chances for the Gunners in the Premier League since August 2014 than Sanchez (272).
- In all competitions, Sanchez has scored 80 goals and been involved in 121, more than any other Arsenal player since August 2014.
- Arsenal have lost three of the past four Premier League games that Alexis Sanchez has not played any part in - 1-0 at Stoke, 2-1 at Watford and 2-1 against Bournemouth.
- Mkhitaryan has made 63 appearances for United - 22 this season - scoring 13 goals.
'Good business for both clubs' - What they said
Former England and Newcastle striker Alan Shearer: "I think it is good business for both clubs.
"Arsenal are getting rid of a player who doesn't want to be there, but they are also getting a player whose face maybe didn't fit at United, but who is much better than he's shown at United."
Ex-Arsenal striker Ian Wright: "The way Sanchez is playing [this season], I can't see how it is going to hurt Arsenal."
Former Manchester United striker Dwight Yorke: "Having a player of that quality added to our squad, with the great ability we've already got up front, this will be an absolutely fantastic deal for us to get such a quality player."
Ex-Manchester United and Stoke defender Danny Higginbotham: "He's that match-winner. I'm not comparing him to Eric Cantona but he's one of them that can turn possibly a drab 0-0 into a 1-0."
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