US international Aidan Morris has completed the formalities of his move from MLS side Columbus Crew.
The 22-year-old midfielder has signed a four-year contract with the club after jetting in from the States this week.
The highly-rated Morris arrives with over 100 appearances for Crew under his belt and has a burgeoning reputation as a tough tackling athletic midfield man.
Born in Florida, Morris represented the US at U18, U21, and U23 before making his senior debut against Serbia in January 2023.
Boro head coach Michael Carrick said: “We're delighted to welcome Aidan to the club. He's a good player.
"He suits our style of play, he's strong, he likes to get on the ball, and he plays off both feet.
"He's a good age, but he's already had a taste of success and he has a good amount of experience.
"We're excited to work with him."
Morris becomes the club's third signing of the summer after Luke Ayling and Delano Burgzorg.