Luke Shaw has become the most expensive teenage footballer in history after he completed his £27m move to Manchester United.
Shaw, 18, passed a medical at the club's Carrington training ground and signed a four-year contract, with the option of another year.
The deal is understood to be worth £27m, plus add-ons. That figure eclipses the £25.6m fee United paid for Wayne Rooney in 2004.
"Manchester United is delighted to announce the signing of Luke Shaw from Southampton Football Club," a United statement read.
Despite not turning 19 until July 12, the left-back has already racked up 67 appearances for Saints and three England caps.
The defender now hopes his career can blossom at Old Trafford alongside the likes of Rooney, Robin van Persie and Juan Mata.
"I am thrilled and excited to be joining Manchester United," Shaw said.
"I have been at Southampton since I was eight-years-old and I would like to thank them and the fans for everything they have done for me.
"I want to continue to progress my career and joining United is the ideal place for me to do that.
"I am looking forward to this new chapter in my life and also looking forward to learning from the world class players and management at the Club."
The add-ons in the deal could take the figure beyond £30m.
That may seem excessive for such a young player, but United assistant manager Ryan Giggs is sure the club have bought one of the best prospects in English football.
"Luke is a very talented young left-back with great potential," said Giggs, who will work under new manager Louis van Gaal next season.
"I am delighted he has joined Manchester United as I believe this is the right Club for him to continue his development as a young player and eventually fulfil that promise."
Van Gaal made his first United signing on Thursday when he purchased Ander Herrera from Athletic Bilbao.
Meanwhile, Adam Lallana is on the verge of following fellow England World Cup squad member Luke Shaw out of Southampton, with a move to Liverpool understood to be close.
Lallana was due on Merseyside for a medical yesterday and, should he sign, would link up with striker Rickie Lambert, who joined Liverpool from Southampton just before the start of the World Cup.
The move would end Lallana's 14-year association with Southampton, having joined from Bournemouth in September 2000, aged 12. That deal included a 25 per cent sell-on clause, which means that the Cherries are set for a cash windfall from the reported £25m move.
He was identified as manager Brendan Rodgers' primary target for the summer window and the club tried to get a deal done before the World Cup.However, because of the turmoil at St Mary's after the departure of manager Mauricio Pochettino, Saints were not prepared to let any players leave until they had appointed a replacement.
Lambert, though, was allowed to move as Southampton classed that as a special case, as the striker was returning to his boyhood club.