Former West Ham and Ipswich manager John Lyall has died at the age of 66.
Lyall led the Hammers to FA Cup victory in 1975 and 1980
Lyall suffered a heart attack on Tuesday night, which resulted in his sudden death.
He succeeded Ron Greenwood as boss at Upton Park in 1974 and was in charge until June 1989. He took over at Ipswich the following year.
Lyall won the FA Cup twice with West Ham, in 1975 and 1980, before leading Ipswich to promotion to the inaugural Premier League in 1991/92.
The Hammers beat Arsenal in 1980 to lift the FA Cup as a team from the old Second Division - and they are the last club to achieve such a feat from outside English football's top echelon of clubs.
Trevor Brooking scored West ham's winner against the Gunners and he said: "It's a huge shock.
"He was a much-loved figure at Upton Park and had a lasting influence on the club's development and the way the team played.
"Like Ron Greenwood before him, he encouraged good, open attacking football and all West Ham fans will be deeply shocked by the news.
"He was a man of great integrity and loyalty and anyone who knew him would have nothing but good things to say about him.
"He recently attended a players' reunion and was easily the most popular man that evening. Everyone wanted to talk to him. I think everyone in football will feel a sense of loss and our thoughts at the moment are with his wife and family."
Lyall originally joined West Ham as a groundstaff boy in 1955 before graduating through the ranks to play as a left-back and he made his debut against Chelsea in 1960.
But knee problems forced him to end his playing career early aged 24 and this heralded Lyall's first steps into coaching.
Lyall was guided by his managerial mentor Greenwood at West Ham for three years prior to taking charge of West Ham and his spell at the helm ended following relegation from the old First Division in 1989.
He assumed the helm at Ipswich the following year but, after his initial success at Portman Road, he left the club in December 1994 and never returned to football management.
West Ham will play Middlesbrough in an FA Cup semi-final on Sunday and current boss Alan Pardew told the club's website: "It is another very sad day for West Ham United after the loss of Ron Greenwood only two months ago.
"Like Ron, John did so much to build the footballing beliefs and values that this club is built on.
"To win the FA Cup twice and lead the club to its highest league finish tells you just how much of an impact John Lyall made on the history of West Ham United - and his contribution will never be forgotten.
"I am sure that our supporters will pay tribute to John's memory in a fitting manner at our FA Cup semi-final at Villa Park on Sunday and we as a team will do the same."
Ipswich added their commiserations following the news of Lyall's death.
"It is with deep regret that Ipswich has learnt of the death of John Lyall," said a statement from the club.
"As first-team boss, he masterminded the club's promotion to the new Premiership in 1992 and remained in charge for a further two years.
"The thoughts of everyone at the club are with his family at this sad time."