Cardiff have completed the signing of ex-Saints academy goalkeeper Simon Moore from Brentford on a four-year deal.
City manager Malky Mackay had previously confirmed a deal had been agreed with the Bees, with the 23-year-old becoming a Bluebird yesterday after the necessary paperwork was completed.
Moore, from the Isle of Wight, is set to be quickly reunited with his former team-mates as Cardiff travel to face Brentford in a pre-season friendly tonight.
Moore started his career in the Saints academy and had a spell with Farnborough Town before joining Brentford in 2009. He kept 13 clean sheets in 52 appearances last term.
Mackay said: "We have been watching Simon for a year or so - he is a real up-and-coming goalkeeper. "My thanks go to Brentford for the way they went about their business and we are delighted to get Simon in for the start of our season.
"He is one for the future and we have three quality senior goalkeepers in our squad."
Moore becomes Cardiff's third summer acquisition as the club prepare for their maiden Premier League season, striker Andreas Cornelius and defender John Brayford having already arrived at Cardiff City Stadium.
The Welsh club have also had an offer of around £9.5million accepted for Toulouse's French international midfielder Etienne Capoue, and are hoping to convince the 25-year-old his future lies in south Wales, despite reports he is keen on a move to Spain.