Manchester United manager Alex Ferguson is to retire at the end of the season.
United confirmed the news on their website this morning.
"The decision to retire is one that I have thought a great deal about and one that I have not taken lightly," said Ferguson, 71.
"It is the right time."
He will continue as director and ambassador for the club.
Ferguson's last game in charge will be at West Bromwich Albion on 19 May and he will join the club's football board.
"It was important to me to leave an organisation in the strongest possible shape and I believe I have done so," he said.
"The quality of this league winning squad, and the balance of ages within it, bodes well for continued success at the highest level whilst the structure of the youth set-up will ensure that the long-term future of the club remains a bright one."
Now, for the first time in over a quarter of a century, United are on the hunt for a new manager.
David Moyes, out of contract at Everton, and Jose Mourinho, who is expected to leave Real Madrid at the end of the season, are the obvious favourites, although Borussia Dortmund's highly-regarded coach Jurgen Klopp and Bayern Munich's 67-year-old outgoing boss Jupp Heynckes will also come into contention.
It promises to be a major test of nerve for the Glazer family, plus Ed Woodward, who will replace David Gill as chief executive in the summer.
"Alex has proven time and time again what a fantastic manager he is but he's also a wonderful person," said co-chairman Joel Glazer.
"His determination to succeed and dedication to the club have been truly remarkable.
"I will always cherish the wonderful memories he has given us, like that magical night in Moscow."
Avi Glazer added: "I am delighted to announce that Alex has agreed to stay with the club as a director.
"His contributions to Manchester United over the last 26 years have been extraordinary and, like all United fans, I want him to be a part of its future."
"The decision to retire is one that I have thought a great deal about and one that I have not taken lightly. It is the right time."
Former United striker Dwight Yorke, who played under Ferguson between 1998 and 2002 and was part of the 1999 treble-winning side, feels a combination of factors led the Scot to call it a day at the age of 71.
"I've seen Sir Alex Ferguson on Monday at a charity game," the former Trinidad and Tobago international told Sky Sports News.
"He was in good spirits, but the rumours were really strong around the place that he was going to retire and there was a big announcement supposed to be happening tomorrow and not today.
"I think probably the fact of the club floating on the stock market meant this decision needed to come out very quickly.
"But the people within the football club knew this was likely to happen this season. And I think with his hip replacement (booked in for late July), with David Gill going as well, that sort of pushed him to say 'this might be the best time for me to retire'."
Alex Ferguson statement
"The decision to retire is one that I have thought a great deal about and one that I have not taken lightly. It is the right time.
"It was important to me to leave an organisation in the strongest possible shape and I believe I have done so.
"The quality of this league winning squad, and the balance of ages within it, bodes well for continued success at the highest level whilst the structure of the youth set-up will ensure that the long-term future of the club remains a bright one.
"Our training facilities are amongst the finest in global sport and our home Old Trafford is rightfully regarded as one of the leading venues in the world.
"Going forward, I am delighted to take on the roles of both Director and Ambassador for the club.
"With these activities, along with my many other interests, I am looking forward to the future.
"I must pay tribute to my family, their love and support has been essential.
Alex Ferguson's post-match press conference from the Airtricity XI v Manchester United in 2010
"My wife Cathy has been the key figure throughout my career, providing a bedrock of both stability and encouragement. Words are not enough to express what this has meant to me.
"As for my players and staff, past and present, I would like to thank them all for a staggering level of professional conduct and dedication that has helped to deliver so many memorable triumphs.
"Without their contribution the history of this great club would not be as rich.
"In my early years, the backing of the board, and Sir Bobby Charlton in particular, gave me the confidence and time to build a football club, rather than just a football team.
"Over the past decade, the Glazer family have provided me with the platform to manage Manchester United to the best of my ability and I have been extremely fortunate to have worked with a talented and trustworthy Chief Executive in David Gill.
"I am truly grateful to all of them.
"To the fans, thank you. The support you have provided over the years has been truly humbling. It has been an honour and an enormous privilege to have had the opportunity to lead your club and I have treasured my time as manager of Manchester United."
FERGUSON'S 49 TROPHIES
Spanning almost four decades, from humble origins at St Mirren, it is hard to imagine anyone getting close to the records Ferguson has set.
Scottish First Division (1): 1976-77.
Scottish Premier Division (3): 1979-80, 1983-84, 1984-85.
Scottish Cup (4): 1981-82, 1982-83, 1983-84, 1985-86.
Scottish League Cup (1): 1985-86.
European Cup Winners' Cup (1): 1982-83.
European Super Cup (1): 1983.
Manchester United Premier League (13): 1992-93, 1993-94, 1995-96, 1996-97, 1998-99, 1999-2000, 2000-01, 2002-03, 2006-07, 2007-08, 2008-09, 2010-11, 2012-13.
FA Cup (5): 1989-90, 1993-94, 1995-96, 1998-99, 2003-04.
League Cup (4): 1991-92, 2005-06, 2008-09, 2009-10.
Charity/Community Shield (10): 1990 (shared), 1993, 1994, 1996, 1997, 2003, 2007, 2008, 2010, 2011.
Champions League (2): 1998-99, 2007-08.
European Cup Winners' Cup (1): 1990-91.
European Super Cup (1): 1991.
Intercontinental Cup (1): 1999.
FIFA Club World Cup (1): 2008.