Former England U20 lock Stan South joined the club on a short term loan from Exeter Chiefs in February 2020.
South, 23, makes the move north from Sandy Park, whom he joined from Harlequins at the start of the current campaign.
The 6ft 5in former England U20 lock made three appearances for the 2016/17 Premiership Champions before joining the capital club.
The Southampton-born lock came through the ranks at Stanley Park School where he showed leadership abilities from a young age.
South captained Sutton and Epsom U16s, Surrey U16s and U17s, Whitgift first XV as well as Harlequins U18s, before joining the London club on a full-time contract.
South debuted for the Londoners against Gloucester in 2015, while he had previously been nominated for the Anglo-Welsh Cup Breakthrough Player of the Year award following some outstanding performances for the club at both lock and in the back-row.
Date of birth: 24 July 1996
Place of birth: Southampton