Manchester United have confirmed the signing of Luke Shaw from Southampton on a four-year contract with the option to extend for a further year.
The England international left-back indicated that his 27 million pound move from Southampton had been completed earlier on Friday by changing his Twitter biography to: "Professional footballer at Manchester United football club."
The 18-year-old travelled up to Manchester on Thursday to have a medical and agreed personal terms with United after the two clubs were in talks about a fee.
Shaw told Manchester United's official website: "I am thrilled and excited to be joining Manchester United. 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."
United assistant manager Ryan Giggs added: "Luke is a very talented young left-back with great potential. He has developed immensely during his time at Southampton and has all the attributes to become a top player. 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."
Shaw's arrival follows the 28.8 million-pound signing of Athletic Bilbao midfielder Ander Herrera on Thursday as United, after a slow start to their summer transfer business, have become heavy spenders.
The completion of Shaw's transfer ends United's long search for a new left-back. Former manager David Moyes failed in attempts to sign Everton's Leighton Baines and Real Madrid's Fabio Coentrao last summer.
Shaw was scouted by Moyes and, while new manager Van Gaal opted not to pursue some of the targets the Scot had identified, United continued to pursue the Southampton player.
Shaw's fee will make him Southampton's club-record sale and the second member of England's World Cup squad to leave St Mary's this summer after striker Rickie Lambert joined Liverpool.
Meanwhile, speaking to Paddy Power before the transfer was completed, former United midfielder Paul Scholes claimed the size of the fee paid for Shaw was bad for English football.
He said: "The proposed 34 million pound transfer for the 18-year-old Luke Shaw to Manchester United is another example of something which has a bad long-term impact.
"Clubs are priced out of this market which is why they go abroad for cheap options -- they're not better players. For a left-back to be worth 34 million pounds shows how silly the game has gone. For that money I want a centre-forward who's going to score 30 goals a season."
Despite Scholes' remarks, United insist the transfer fee is less than 34 million pounds.