Uruguayan international Gaston Ramirez has completed a move to Italian side Sampdoria.
Ramirez joins the Serie A side after spending 18 months as a Boro player.
The 26-year-old made 44 appearances for Boro after joining initially on loan from Southampton in January 2016.
He scored seven goals in 18 league appearances as the club clinched promotion from the Championship in May 2016.
Last season, Ramirez scored twice in 26 appearances, but his final outing in a Boro shirt came in a 4-0 defeat at Bournemouth when he was sent-off during the first half after being shown two yellow cards.
Due to a privacy clause within the transfer deal we are unable to make the fee public.