Northern Ireland international Paddy McNair has completed his move from Sunderland to north-east neighbours Middlesbrough.
The two clubs agreed a fee of around £5m last week, and McNair has now agreed a four-year deal with the Championship side.
Brighton were initially in the running to sign the 23-year-old but they had two bids rebuffed, the second of which was believed to be for £3.5m.
McNair made 18 appearances and scored five goals for Sunderland last season but he could not help them avoid relegation to Sky Bet League One.
He broke into Manchester United's first team in 2014, making 24 Premier League appearances.
McNair went on to make his international debut in 2015 and was part of Michael O'Neill's squad that reached the last 16 at Euro 2016.