Manchester United have completed the signing of striker Romelu Lukaku from Everton.
The Belgium international has signed a five-year contract at Old Trafford after United had agreed a fee, believed to be an initial £75m, with the Toffees on Saturday.
Lukaku, who scored 25 Premier League goals last season, will now link up with Mourinho's squad in Los Angeles ahead of pre-season training.
The former Chelsea man has been training in LA with new team-mate Paul Pogba and replaces Wayne Rooney in United's squad, with the Red Devils' record goalscorer moving the other way.
"I would like to start by thanking Everton and the fans for the last four wonderful seasons, I have made some special friends and we have shared some amazing moments," Lukaku told United's official website.
"However, when Manchester United and Jose Mourinho come knocking at the door it is an opportunity of a lifetime and one that I could not turn down.
"You could see the fight, determination and the spirit in this team during the Europa League final and I want to become a part of that.
"I cannot wait to run out at Old Trafford in front of 75,000 fans but before that pre-season is where the hard work starts and I am looking forward to that first training session."
Manager Jose Mourinho, who sanctioned Lukaku's departure from Chelsea to Everton, says the player is ideal for Old Trafford.
"Romelu is a natural fit for Manchester United," he added.
"He is a big personality and a big player. It is only natural that he wants to develop his career at the biggest club. He will be a great addition to the group and I know they will make him very welcome. I am really looking forward to working with him again."