Manchester United signed Chile forward Alexis Sanchez from Arsenal in a swap deal with midfielder Henrikh Mkhitaryan after a protracted transfer saga finally ended on Monday.
The 29-year-old Sanchez, who was out of contract at Arsenal at the end of the season, has joined the Old Trafford club after local rivals Manchester City had pulled out of the race.
British media reported that Sanchez, who will wear United's iconic No. 7 shirt, has joined the club on a four-and-a-half-year deal, while Arsenal announced that Armenia captain Mkhitaryan, who turned 29 on Sunday, had signed a long-term contract.
Sanchez said: "I am thrilled to be joining the biggest club in the world. 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 missed Arsenal's 4-1 win over Crystal Palace on Saturday to have a medical in Manchester on Sunday.
He would have been available on a free transfer when his contract expired in four months' time but once City baulked at the amount of money involved in a mid-season deal, United manager Mourinho urged his club to step in.
Mourinho lauds Sanchez
"Alexis is one of the best attacking players in the world and he will complete our very young and talented group of attacking players," said Mourinho.
"He will bring his ambition, drive and personality - qualities that make a Manchester United player and a player that makes the team stronger and the supporters proud of their club's dimension and prestige."
United are second in the domestic standings, 12 points behind Manchester City, and will hope Sanchez can help them cut the gap on their neighbours whilst also helping them progress in the Champions League, where they face Sevilla in the last 16.
Sanchez almost joined City at the end of the August transfer window but that deal fell through as Arsenal manager Arsene Wenger was unable to sign a replacement in time.
He scored 80 goals in 166 appearances after the London club paid 35 million pounds ($48.83 million) for him in July 2014, and won the FA Cup in 2015 and 2017, scoring in both finals.
Missing out on the Champions League this season was a bitter disappointment, however, followed by another blow when Chile failed to qualify for this year's World Cup finals.
A move to either of the Manchester clubs became a preferable option to signing a new contract. Arsenal wanted Mkhitaryan in exchange and he was delighted to join the London club.