Southampton have turned Ryan Bertrand's loan deal from Chelsea into a permanent transfer.
Bertrand originally moved to the St Mary's Stadium on season-long loan deal in the previous transfer window.
The 25-year-old has subsequently done enough to convince Ronald Koeman to hand him a four-and-a-half-year deal.
Bertrand broke into Chelsea's first-team in April 2011 and played in the club's UEFA Champions League final victory over Bayern Munich in May 2012.
However, the England international struggled for game time when Jose Mourinho returned as Chelsea manager ahead of the 2013-14 season and spent the second half of that campaign on loan at Aston Villa.
After Southampton sold Luke Shaw to Manchester United in a big-money move in the last transfer window, Koeman acted swiftly to bring in Bertrand.
He has since started 22 of Southampton's 23 Premier League matches, scoring twice, although he will sit out the club's next three games after receiving a straight card in Sunday's 1-0 loss to Swansea City.
The Bertrand deal rounds off a productive transfer deadline day for Southampton, after the south coast club also landed Filip Djuricic on loan from Benfica earlier on Monday.