West Ham have signed central defender Matthew Upson from Birmingham City for an initial fee of £6m.
Defender Upson was keen to move away from Birmingham
Upson, 27, has signed a four-and-a-half year deal and the fee could rise to £7.5m based on appearances.
Birmingham had rejected bids of £4m and £6m for Upson, who had made it clear he would not extend his deal after it ran out at the end of next season.
Upson was signed by the Blues in a deal worth £2.5m from Arsenal and they will get 25% of the profit.
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Birmingham were stubbornly determined to keep hold of him as they challenge for automatic promotion straight back into the Premiership after relegation last season.
But they have buckled at the latest bid from West Ham and Upson becomes Hammers boss Alan Curbishley's sixth signing during the January transfer window.
This is just simply about player power and the player clearly did not see his future with us
Birmingham chairman David Gold
"This is not and never has been about money," Blues chairman David Gold told his club's website.
"It was always about Matthew doing the right thing and honouring his contract: as we did when he was out injured for the past year."
He added: "This is just simply about player power and the player clearly did not see his future with us.
"He and his agent campaigned to the board for him to leave.
"Birmingham wishes to have its team populated by players committed to achieving Premiership status with Birmingham and remaining at the club thereafter."
The former England Under-21 international joins Luis Boa Morte, Lucas Neill, Calum Davenport, Nigel Quashie and Kepa Blanco as January transfer window arrivals at Upton Park.
Curbishley has been busy bringing in players as he tries to steer the club to Premiership safety.
They are currently third-from-bottom and two points adrift of fellow relegation-battling Wigan.