Southampton have signed full-back Ryan Bertrand from Chelsea on a permanent deal, the club have confirmed.
Bertrand, 25, joined the south coast club on loan at the beginning of the season and swiftly became a fixture at left-back under Ronald Koeman.
The defender has signed a four-and-a-half year contract at St Mary's, keeping him at the club until 2019.
"We thank Ryan for his service and wish him the best of luck for the future," Chelsea wrote on their official website.
Bertrand was one of two long-term departures from the Blues on transfer deadline day after Andre Schurrle returned to Germany after signing for Wolfsburg in a deal reportedly worth £22m.
While Bertrand was part of the side that won the Champions League with Chelsea in 2012, he struggled to win over Jose Mourinho following the coach's return to Stamford Bridge in the summer of 2013.
Having become an integral member of the Southampton first team since his arrival in July, a longer stay quickly became an option for the player, who hinted back in October he would have no problems in signing a permanent deal on the south coast.
"It is one of them things where I've got to wait and see, but, for me, there's no reason why not, to be honest," Bertrand told Sky Sports.
"There is a good base to the club, we're pulling in the right direction. We have fantastic fans, fantastic players, a fantastic manager and the coaching staff."
On transfer deadline day, Southampton also strengthened their bid to crash the top four with midfielder Filip Djuricic, who joined the club on loan for the rest of the season from Benfica.
The 23-year-old Serbian international terminated his loan deal with Bundesliga side Mainz before making his move to the Premier League.
Southampton also have the option to make Toby Alderweireld's stay at the club a permanent one, as revealed by Koeman in January. The on-loan Atletico Madrid defender is another to have swiftly become a first teamer at the club but there has yet to be any movement in tying the Belgian down to a permanent deal.