Chelsea have reached an agreement with Stuttgart regarding the sale of Khalid Boulahrouz.
The Dutch defender endured a disappointing two-year spell with the Blues, failing to establish himself as a regular member of the first-team squad.
He spent the whole of last season on loan at Primera Liga side Sevilla, but again failed to impress.
However, a number of eye-catching displays at Euro 2008 saw him thrust back into the limelight and he is thought to have cost his new German employers around £4million.
The 26-year-old has previously enjoyed considerable success in the Bundesliga during his time at Hamburg and will be hoping to recapture that form on his return.
A statement on Chelsea's official website read: "We would like to thank Khalid for his contribution while he was with Chelsea FC and would like to wish him luck at his new club."