Cristiano Ronaldo has led a wave of Twitter tributes from his fellow former Manchester United players and figures around the sporting world after Sir Alex Ferguson's retirement.
Ferguson announced his retirement after 27 years in charge at Old Trafford this morning, and the Portuguese star - whom Ferguson sold to Real Madrid for £80million in 2008, led the way.
Ronaldo's message was simple - he posted a picture of his first day at Old Trafford with Ferguson in 2003 with the message 'Thanks for everything, Boss.'
'I'm shocked - I just can't make sense of the timing,' he told Sky Sports News. 'It has come as a bombshell, I really don't know what to make of it.
'Yesterday I was really happy with what he had done this season, now this, I'm disappointed and very sad.
'He's always said the day would come when something in his life wasn't right, is it is hip operation (he will have this summer)? I can't see him retiring over that.
'(Until) he explains why, we can guess and guess.
'There is something there we don't know about, he won't retire for the sake of retiring, it is difficult to makes sense of it.'
The Great Dane's team-mate Bryan Robson also expressed his astonishment at the announcement, saying: 'It came as a surprise.' He's probably the greatest manager there's ever been. To be at Manchester United for 27 years is a magnificent achievement never mind to win what he's won.
'I'm sure there are good reasons, whether its to put his feet up and spend more time with the grandkids and have more family time, I don't know.
'He was always the first in to the training ground. Nothing's been said at the club about a successor but like everything at Manchester United they will probably know in their own minds who the next manager will be, because it's going to be an unbelievably hard task for whoever it is.
'One thing going for them is that the club has the structure in place for continuity. There's not much work to do on that side of things.'
A United legend from even further back, Denis Law, said he doesn't know why Ferguson chose now to retire.
'I was extremely shocked. I couldn't believe it. I was with him only last week in Manchester. I always thought he would go on until 90 and then say: 'that's it'. He's too young to retire,' said Law.
'Who will take over, I don't know? Who takes over from the most successful manager of all time? Its a difficult job for anybody but he has left Manchester United in a strong position. Whoever comes will be given time.
'I've no idea why he's taken the decision. His life is football. The good thing about Sir Alex is that he's never changed after all this success. He always knew the future of the club was about getting good young players into the club. He has created three to four great teams within his time.'
Former United striker Louis Saha also paid tribute to Ferguson: 'Wow S A Ferguson leaving. Hope is [sic] health ok. He is the most powerful man i ever met in my life after my dad. Huge respect for Football God.'
Fellow former Old Trafford striker Michael Owen also took to Twitter to show his appreciation for his former manager.
He posted: 'It's just not sinking in! Manchester United with no Sir Alex just doesn't feel right. What a man and great that it has ended on his terms. What a privilege to have played under arguably the best manager the world has ever seen.'
Former United reserve player Bojan Djordjic tweeted: 'Will never forget mornings at Carrington in Sir Alex office. He used to show us in the youth team videos of him elbowing defenders! #legend'
Figures from around the game also spoke out in tribute of Ferguson, including FIFA chairman Sepp Blatter, who said: 'Was honour to present Sir Alex with Award at 2011 Ballon D'Or. Will his longevity at the top ever be repeated?'
England manager Roy Hodgson said the news was a blow to football.