Alexis Sanchez has completed his move from Arsenal to Manchester United, with Henrikh Mkhitaryan moving in the opposite direction in a swap deal, the clubs have announced.
The 29-year-old Chile forward arrives at Old Trafford after three-and-a-half years at the Emirates.
"I am thrilled to be joining the biggest club in the world," Sanchez said on the United website.
"I have spent three-and-a-half wonderful years at Arsenal and I bring with me very positive memories of that great club and its fans.
"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."
The perfect #MondayMotivation! 👌
— Manchester United (@ManUtd) January 22, 2018
@Alexis_Sanchez #Alexis7 pic.twitter.com/XV1u2VOHvr
Mourinho 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 and a player that makes the team stronger and the supporters proud of their club dimension and prestige."
Arsenal said Mkhitaryan (also 29) had signed "a long-term contract".
Love that, @HenrikhMkh - we're delighted to have you here 🔴 pic.twitter.com/PDABMfhsNx
— Arsenal FC (@Arsenal) January 22, 2018
The Armenian said: "I'm very happy that we could finish this deal and I'm very happy to be here. It's a dream come true because I've always dreamed of playing for Arsenal. Now that I'm here, I'll do my best for this club to create history."
Arsene Wenger added: "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."