Williams: Folau could have made it in AFL
But Williams says the club reneged on its promise to make him Sheedy's successor, leading to his sudden departure a year before the club made Leon Cameron its second coach.
The Port Adelaide premiership coach also revealed he believed Israel Folau would have made it as an AFL star, stunned by his new polarising persona as he goes to war with Australian rugby.
The Giants eventually offered Williams a contract of only $100,000, forcing him to move on when it became apparent they would not allow him to replace Sheedy.
The only man to be at foundation clubs GWS, Brisbane and Port Adelaide confirmed to the Herald Sun's Sacked podcast the club's confidential arrangement where he actually coached the Giants.
"I knew what I was getting into but I thought I was going to be coach and that's the reason I went there," he said.
"When I was told, 'You are still getting paid by Port Adelaide, we are not going to pay you very much', that's the AFL's take on it.
"We met with Gubby (football boss Graeme Allan) and Gubby said 'Sheeds is going to do all the promotional stuff, you will do all the reviews, you will do all the planning, you will do all the mentoring of the other coaches', it's what a senior coach does.
"And that's what I was doing.
"At half time sometimes Sheeds would be talking to the corporate people and I would be talking to the players and Sheeds would come down and put the players in their spots.
"Those were the things happening behind the scenes but, to Sheeds' credit, he let me do what I do best and I certainly let him do what he does best and he was outstanding for the club.
"(But) I wanted this club with the best young players in Australia who only have one window to be great, I wanted them to have the best facilities and set-up and the other coaches were Chad Cornes and Dean Brogan and Luke Power who had never coached one day in their life coaching these young people."
It eventually became clear to Williams the club would not make him their senior coach despite his expectation he would succeed Sheedy.
"I was getting paid $200,000 to do all that and so, having been told I am going to be the next senior coach, I said, OK, I will take $300,000 the first year and $200,000 the second.
"But, in the last year, they said 'we are going to go with Sheeds again'.
"I said 'just re-do my contract which confirms the year after I will be the senior coach and give me an extended contract'.
"They wouldn't extend my contract, it was going to be a $100,000 contract, at the end of the year, that's it."
Williams is a famed developer of talent going back to his days at Essendon's VFL team and believes rugby code-hopper Israel Folau needed better coaching around him to thrive after being lured from rugby to play AFL.
"It was money well spent. He would get on the front and back pages of the papers regularly.
"He is probably the nicest, quietest, most respectful person I have ever met.
"So with the coaches we had to actually help him, we probably didn't give him his best chance.
"If I cut the best stuff out he did, you would go, 'Wow'.
"This is from a person who saw Matthew Lloyd at 16 or 17 coaching at Essendon and saying, 'I see something in him'.
"I still see something in Israel and I thought he would go on to make it on one or two more years … with continually better coaching and better resources and all the things we didn't have at the time.
"He joined in and tried very, very hard and now I am disappointed with how it has come around that everyone is very polarised on him. As a person he is one of the nicest people I have met."