Burnley have signed Jack Cork from Swansea City on a four-year deal.
The fee is undisclosed, but reports believe it could rise up to £10m.
Cork spent an 18-month loan spell with the Clarets across 2010 and 2011 while he was on the books at Chelsea, making 57 appearances for the club during that stint.
The London-born midfielder moved to Southampton after his time at Turf Moor, and spent four seasons there before moving to Swansea.
"It's good to come back and try and have another go here, especially in the Premier League. It's a new challenge for me and one I'm excited for and I'm looking forward to meeting new people," Cork told the club's website.
"It's great to be back. I've got some great memories from the year-and-a-half I was here and it's good to come back and see some old faces."
SIGNING: Jack Cork has signed a four-year deal with the Clarets.
More to come.... pic.twitter.com/UMeIATVExl
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