Defender Jonny Burn has joined Bristol Rovers.
The 21-year-old has departed Boro to join the League One club on a permanent basis.
Darlington-born Burn first joined Boro from Sunderland, initially as a scholar. He was awarded a professional contract in the summer of 2014.
He had impressed on loan spells with Oldham Athletic last season, and Scottish Premiership club Kilmarnock earlier this campaign.