Boro have signed Jack Stephens on a season-long loan from Southampton.
The 21-year-old Cornwall-born central defender began his career with Plymouth Argyle before joining the Saints in 2011.
He made 42 appearances on loan to Swindon last season and featured in the League 1 Play-Offs for the Robins.
2014/15 was Stephens' second spell with the Wiltshire club having made 10 appearances for them towards the end of the previous season.
Stephens has represented England at under-18, under-19 and under-20 level.