Boro have completed the signing of Micah Hamilton from Manchester City.
The 20-year-old joins the club on a four-year contract and trained with his new team-mates for the first time on Friday morning.
The Manchester-born attacking midfielder is a graduate of the Man City Academy, and progessed from the U18s and U21s to make his senior debut in the Champions League, scoring his first goal in a 3-2 win against Red Star Belgrade.
Micah, who has played in the number 10 role and out wide, has also won England honours at U16 and U20 level.
Boro head coach Michael Carrick said: "Micah is an exciting young player who we're looking forward to working with. He's already been in and around the senior side at Man City - he's got that experience from playing in the Champions League - and he is another great addition to the squad."
The youngster follows Luke Ayling, Aidan Morris and Delano Burgzorg as the club's senior signings this summer.