West Ham have confirmed Tomas Soucek has joined the club on a permanent deal and signed a four-year contract.
The Czech Republic international midfielder has impressed since arriving at the London Stadium in January on loan from Slavia Prague.
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West Ham held an option which allowed them to sign Soucek permanently for a fee of £15m as long as they avoided relegation from the Premier League. That is on top of a £4m loan fee Slavia have already received.
The Hammers moved quickly to sign Soucek after securing their Premier League status with a 1-1 draw against Manchester United on Wednesday and Hammers boss David Moyes is pleased to have the 25-year-old's future sorted.
Moyes told Sky Sports News: "I have always believed it would be a permanent deal because I knew it was subject to us being in the Premier League and I always felt that we would be a Premier League club so I never really had any great worries about Thomas.
"The biggest concern was how well and how quickly he could fit into the Premier League. I think all the other things connected to him were good - he could score, he could run, he was a good footballer. So it was more to see how he would fit in.
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"I was always confident he would be here with us. But I am glad to get it out of the way because I've been asked the question a few times.
"Obviously, we are glad he is going to be a West Ham player for a good period to come."
Soucek has scored three goals in 12 Premier League appearances for West Ham so far this season.
Moyes is pleased with how he has fit in alongside Declan Rice and Mark Noble in West Ham's midfield.
"The best thing about him is he is a terrific lad. He has got very good physical capabilities," Moyes added.
"He has scored some really important goals for us. He scored against Chelsea and he scored against Watford so he has got us some really important goals recently and maybe could have scored a couple more as well.
"When we came in in January, we were talking about needing another midfield player. I thought we needed somebody else who could help Declan and Mark Noble. I have to say, I think Thomas has been a really good fit."