Tomas Soucek has signed a four-year-deal to make his move to West Ham permanent.
The Czech midfielder, who joined on loan from Slavia Prague in January, has been key to West Ham's successful relegation fight, adding three goals to his impressive performances since the restart.
The Hammers have paid just north of £19million in total for Soucek, including the £4million loan fee agreed in January.
"I've always believed he would be here on a permanent deal because it was subject to us being a Premier League club and I always felt we would be a Premier League club," said Moyes.
"I never really had any concerns with Tomas [staying], the biggest concern was how well would he start and fit into the Premier League quickly, all the other things connected to him have been good: he can score, run, help us - he's a good footballer.
"The best thing about him is he is a terrific lad. He has scored some really important goals for us, he could have got a couple more as well.
"When I came in we were talking about needing someone to help Declan and Mark Noble and I have to say Tomas has been a really good fit for them."
