The 28-year-old England international put pen to paper on a four-year contract to end his six-year stay at Charlton following their relegation from the Barclays Premier League at the end of last season.

He follows Jonathan Woodgate, Jeremie Aliadiere and Tuncay Sanli to the Riverside Stadium, with Southgate now chasing further targets.

However, Young's capture fills a major gap in the squad with fellow right-backs Abel Xavier and Stuart Parnaby having been released at the end of the last campaign.

The Harlow-born player had made no secret of his wish to return to the top flight and travelled to Teesside on Monday after Boro were given permission to open talks with him.

He underwent a medical and agreed personal terms and was in the crowd for Tuesday night's friendly victory at Darlington, although his arrival could not be confirmed until all the paperwork was completed today.

Young will be unveiled at a press conference at the club's Rockliffe Park training headquarters tomorrow afternoon.

Southgate will hope he is not the last new face to come in before the start of the new season on August 11 with Manchester United striker Alan Smith back in his sights.

Boro have maintained an interest in the 26-year-old England international throughout the summer, although reports that they have been granted permission to speak to the player have been played down.

United boss Sir Alex Ferguson has hinted the former Leeds player could be allowed to leave Old Trafford, although Smith's representatives and the player himself have maintained throughout the close season that he would rather stay where he is.

Smith is currently in the Far East with United and is expected to seek further talks on his return, but speculation that Everton and Aston Villa could be ready to fight the Teessiders for his signature means they may face stiff competition.

Meanwhile, Boro's 20-year-old defender Matthew Bates will be sidelined for months after managing just 25 minutes of football on his return from serious injury.

Bates, who tore the cruciate ligament and partially tore the medial ligament in his right knee in November last year while on loan at Ipswich, damaged the cruciate ligament in his left knee during the first half of Tuesday's game.

Southgate said: "We all feel for Matty, who was looking forward to playing football again after a long period on the sidelines.

"He had applied himself so well to get back in contention and this latest injury is obviously difficult for him to accept.

"He will get the best possible medical support from us as far as treatment and rehabilitation are concerned and we are all right behind him at this difficult time."