Sunderland youngster Williams Kokolo has joined Middlesbrough after the Black Cats decided against offering him a new contract on Wearside.
The 19-year-old Frenchman, who has been a regular for Sunderland's U23 side this season, was due to be released at the end of the season but has instead signed a two-year deal with Boro.
Kokolo came through the ranks at Monaco before Sunderland brought him to England as a 16-year-old three years ago.
Left-sider Kokolo can play either in defence or on the wing, and he spent a loan spell at Darlington last season when he played nine games for the Quakers before being recalled by the Black Cats.
He did not play a first team game during his time with Sunderland.
Kokolo is, at least initially, expected to link up with Boro's academy and play for their U23 side.
Sunderland are looking to shake-up their own U23 side after a wretched season in Premier League 2.
They have taken a series of players on trial with a view to strengthening their squad, and the latest man to arrive on Wearside is 18-year-old Blackburn Rovers frontman Chanka Zimba.
Zimba has scored eight goals in 13 league games for Blackburn's U18 team this season.
