Centre-back George Edmundson has joined the club on a permanent basis.
The 27-year-old was on a season-long loan from Ipswich Town before being recalled earlier this week.
But a deal has been agreed between the two clubs for George to join Boro on a permanent basis, and he joins on a two-and-a-half year contract.
George made 21 appearances for the club before his recall in midweek.
Already known to Boro fans, Manchester-born George will provide stiff competition across the back-line.
He is a two-time promotion winner, having played a key role in Ipswich’s return to the Championship as well as featuring 10 times in their promotion season back to the Premier League.