West Ham have completed the £16m signing of Bayer Leverkusen striker Javier Hernandez.
The 29-year-old Mexico international arrived in London on Monday to undergo a medical ahead of the transfer and has signed a three-year contract.
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Sky sources understand the striker will become the highest-paid player in the club's history and is set to be on wages totalling £140,000 a week.
"I am very happy to join West Ham United," he said. "For me, the Premier League is the best league in the world and when the opportunity came, I was desperate to sign for this club.
"It was not a difficult decision. West Ham is a historic club, and very ambitious - this summer you can see with the players signed that they are looking to have a very good season.
"I've had three fantastic years playing in Spain and Germany, but England was really the first big chapter in my career and I am so happy to be back.
"I am desperate for the season to start and to help the team achieve all their objectives."
'Chicharito', as he is known, spent four seasons with Manchester United between 2010 and 2015, where he scored 59 goals in 156 appearances, before going on loan to Real Madrid in the 2014/15 campaign.
The two-time Premier League winner left Old Trafford in August 2015 for Germany, where he has been even more prolific, netting 39 times in 76 matches for Leverkusen.
Joint-chairman David Sullivan added: "We are delighted to welcome Javier as the latest fantastic addition to the West Ham United squad.
"Following the arrivals of Pablo Zabaleta, Joe Hart and Marko Arnautovic, he is another top-class professional who brings great experience and quality to the club.
"He has a proven goalscoring record in the Premier League, La Liga and the Bundesliga, as well in the UEFA Champions League and at international level with Mexico.
"We now have some fantastic options in attacking positions and, like all West Ham fans, I am looking forward to seeing Javier score goals in a claret and blue shirt next season."