It is of course not the first time Mourinho has signed the 29-year-old having brought him back to Chelsea in 2014 and having worked with him at Stamford Bridge the Portuguese knows exactly what he will bring to his side.
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"Nemanja is a Manchester United player and a Jose Mourinho player," he told the club's official website. "He represents everything we want in a footballer; loyalty, consistency, ambition, team player.
"I would like to thank him for his desire to join us because without that, it would be impossible to have him here. I am sure our players and supporters will love him. A big welcome to our new number 31."
Matic, for his part, is delighted to be reunited with his former boss and is eager to hit the ground running with his new club.
"I am delighted to have joined Manchester United," he added. "To work with Jose Mourinho once again was an opportunity I couldn’t turn down.
"I have enjoyed my time at Chelsea and would like to thank the club and the fans for their support. I cannot wait to meet my new team-mates and to start training with them.
"This is a very exciting time for the club and I am looking forward to playing my part in creating more history for this great club."
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