Emilio Nsue has joined Championship side Birmingham City for an undisclosed fee.
The Equatoguinean has penned a three-and-a-half-year deal with Gianfranco Zola's Blues.
Having moved to Teesside in August 2014, the versatile 27-year-old made 70 Boro appearances, scoring three goals.
Five of those appearances were in the Premier League this season, the last coming away to Everton in September.
Nsue joins former Boro men Diego Fabbrini, Jonathan Grounds and Lukas Jutkiewicz among City's ranks.