Goalkeeper Angus Gunn has joined Southampton on a five-year deal from Manchester City.
The England U21 international has switched clubs in a deal worth £13.5m, according to Sky sources.
It is understood the deal will see Saints pay £10m plus £3.5m in add-ons.
Gunn told Southampton's official website: "The opportunity was there for me to stay at Manchester City but I saw the potential of this club and the squad.
"The manager and Dave Watson were a big part of the reason why I have chosen to join and speaking to them both was a big factor in my decision.
"I think the club has got a big future and I'm looking forward to getting started now. I've spoken to Dave Watson and he said it would be a great environment to come in to work. It feels really good and I'm buzzing to get going."
Gunn, who graduated from Manchester City's academy, spent last season on loan at hometown club Norwich playing in the Championship.
During his season-long spell at Carrow Road, Gunn made 51 appearances for the Canaries and kept 15 clean sheets.
Southampton manager Mark Hughes said: "Angus is a player who clearly possesses a tremendous amount of potential, but his performances for Norwich and for the England U21 team also demonstrate the capabilities he already has right now.
"We believe he has all the credentials to become a full international goalkeeper for England in the future, and that's exactly the sort of talent we want to have here at Southampton.
"He represents another excellent addition, and we are excited about what he brings to the squad and the further progression we feel he can make with us.
"There was a lot of interest from other teams in the Premier League, so for Angus to choose Southampton as the best option for him is another positive indication of the work the club is doing and what is being built here."
Sky Sports News reported last month that Southampton are listening to offers for goalkeeper Fraser Forster, while current No 1 Alex McCarthy signed a new four-year contract in June.
Gunn could be joined at St Mary's by Denmark international Jannik Vestergaard after Southampton agreed an £18m fee for the defender with German club Borussia Monchengladbach.