West Ham manager Sam Allardyce has paid tribute to a manager he's shared the touchline with no fewer than 45 times, and says Sir Alex Ferguson is possibly the greatest European club manager ever.
Allardyce who has consolidated his West Ham team in the Premier League this season is thought to be very shocked by the retirement of the legendary Manchester United boss.
"I spoke to Sir Alex recently and I had no inkling that he was considering retiring from his position at Manchester United," the Hammers boss told West Ham's official website. "So, like for everyone else, it has come as a bit of a shock.
"I think it's clear he was going to announce this at the end of the season, but whispers have got out somewhere, so he probably had to make it official right now.
"For himself, his wife Kathy and the rest of his family, I hope they can enjoy his retirement, the time they will have together and see things they have always wanted to see."
Allardyce has rebuilt a Hammers side which has picked up some decent results this year with the shrewd signings of Matt Jarvis, Mohamed Diame and Andy Carroll on-loan from Liverpool have earned the club crucial points.
The future of Carroll at the club lies in the balance as the players wage demands might not meet the wishes of co-owners David Sullivan and David Gold.
It's understood the priority signing the Upton Park chairmen want to bring to the club is a striker.
West Ham last met Manchester United in April, and it's fitting the game ended in a 2-2 draw between the gaffers after they've shared touchlines for so many seasons.
"He is the greatest club manager that has ever been produced, certainly in this country, if not Europe," added Allardyce. "However many managers there were before him, the huge task he had was to achieve what Sir Matt Busby had done before him.
"For him to have done that and more, to have won the treble for Manchester United, and the joy and satisfaction of doing that was fantastic.
"To build as many teams as he has built over the seasons, on and off the field, was brilliant. He changed the backroom staff to support what he was trying to do and as a man, he is a fantastic human being.
"We will all sadly miss him, many others will too. Manchester United now have a massive task to replace him."