Fergie's retirement left social media shaken to the core and dominated news feeds and trending topics across the entire world.
Sir Alex Ferguson has conquered social media, having dominated Twitter's trending topics for an entire morning and afternoon - even exceeding the reaction to Margaret Thatcher's death.
Manchester United manager Sir Alex, who has held the post for 26 years, announced his retirement via the football club's official press office Twitter account.
In the hour that followed, the message was 'retweeted' and 'favourited' over 18,000 times, and there were more than 1.4 million mentions of the story on the social micro-blogging network.
The hashtag #ThankYouSirAlex was included in all subsequent tweets from Manchester United accounts, and, within eight minutes of the club's original tweet, became Twitter's biggest trending topic worldwide.
Other related hashtags, including #SirAlex and #MUFC, have dominated the Twittersphere all afternoon. At its peak, the story took eight of the UK's Top 10 trending topics.
As the day went on, there were countless tributes from high-profile football stars, including Vincent Kompany, captain of United's fierce rivals Manchester City.
Even Prime Minister David Cameron got involved in the conversation, but couldn't resist inserting the #AVFC hashtag of his favourite team Aston Villa.
Charles Arthur, technology editor at The Guardian, remarked: "If you want an idea of the reverence with which Sir Alex Ferguson is held, Twitter has an easy guideline: more than Margaret Thatcher, but less - so far - than the new pope."
Sir Alex Ferguson has been manager at Manchester United since taking over from Ron Atkinson on 6 November, 1986. During his time at Old Trafford, he's helped the club to 13 league titles, two Champions League crowns, five FA Cups and four League Cups.
"The decision to retire is one that I have thought a great deal about. It is the right time," said Sir Alex, whose replacement is now the hot topic for discussion.