Premier League strugglers Southampton signed Luton defender James Bree for a reported fee of £750 000 on Thursday.
Saints boss Nathan Jones returned to his former Championship club to land Bree on a three-and-half-year contract.
Jones left Luton to take charge at Southampton in November.
The 25-year-old full-back is Southampton's third signing in the January transfer window after the additions of Mislav Orsic and Carlos Alcaraz
"James is obviously someone who I know well from our time together at Luton, and he has the qualities both on the pitch and also in terms of his character to help us here," Jones said.
"While we have really talented players in the full-back positions, we have been lighter on numbers than we would have liked, so the addition of James to the squad really helps us to address that."
Bree played for Barnsley, Aston Villa and Ipswich before joining Luton in 2019, making a total of 143 appearances for the Hatters.
Southampton sit bottom of the Premier League and lost 1-0 to Newcastle in the League Cup semifinal first leg on Tuesday.
