No Blues fan could believe the news when it came through on Thursday 12 February 1998: Ruud Gullit had been sacked as player-manager. At the time, Chelsea were second in the Premier League, semi-finalists in the League Cup and through to the last eight of the Cup Winners’ Cup; nine months earlier, we had lifted the FA Cup, our first major trophy in 26 years.

If the news that the dreadlocked Dutchman had been let go was not shocking enough, there was another twist in the tale, one that even the canniest of Hollywood scriptwriters would have struggled to dream up. Replacing Gullit at the helm would be Vialli, the Italian striker with whom he had fallen out due to the lack of playing time he’d afforded him.

This wasn’t only back-page news, it was plastered across the front pages of newspapers the following morning, with the focus largely on the decision to sack Gullit – and the betrayal he’d felt – rather than Vialli’s appointment as his replacement.

How had it come to this? Had Gullit’s wage demands led to his demise, or were other factors at play? And what was Vialli’s role?

First, it’s important to establish what had gone on between May 1996, when Gullit was appointed as the club’s new player-manager after effectively being elected by the supporters, and February 1998, when his reign came to an end after only 21 months.

The former World Player of the Year’s first act as Blues boss had been to sign Vialli on a free transfer from the Juventus side he had captained to Champions League glory two days earlier.

Soon, however, Vialli found himself playing second fiddle to Mark Hughes and fellow new signing Gianfranco Zola, a bit-part player less than a year on from being among Europe’s elite. He was afforded a two-minute cameo at the end of the triumphant FA Cup final against Middlesbrough, which looked to be his swansong.

‘I think Ruud was showing me respect there [by bringing him on in the cup final],’ recalled Vialli in 2017, during an interview for the book Blue Day. ‘I don't think he planned to humiliate me by giving me a couple of minutes, I think he probably felt I played a part in the FA Cup, in us getting to the final, and he felt this guy needed to play a little so he'd give me the satisfaction of being involved.

‘From my point of view, I wasn't thinking about leaving. I don't remember thinking I needed to find another club. No – I wanted to come back and show them what I can do.’

The club continued on the same trajectory in the 1997/98, this time with a European campaign to enjoy, and Vialli was indeed showing everyone what he could do as he made a bright start to the season. Ironically, given his struggles the previous campaign, it was at this time that he was considering his future.

‘I was playing more, but I was frustrated with the rotation system which didn't really make sense,’ he said. ‘I was thinking of maybe leaving. My friend Atillio Lombardo was at Crystal Palace and I thought about them, but also Celtic and Glasgow Rangers.’

Instead, he stuck it out – and soon we’d all be talking about the incredible events of one Thursday in February 1998, which sent shockwaves through Chelsea Football Club and English football.

In a BBC column from earlier this year, which included details of his final days as Chelsea boss, Gullit revealed he’d been in negotiations to sign Jaap Stam, who later joined Manchester United, and Brian Laudrup, who did sign for the Blues that summer but lasted only a few unhappy months at the Bridge.

The day before he was sacked, he’d taken to the golf course with a couple of players and a member of staff and found it strange that when he tried to contact Laudrup mid-round, he couldn’t get hold of the Danish winger. It seemed the writing was already on the wall by this point.

‘Ruud's contract was running out at the end of the season and they were talking over a renewal,’ says Vialli, taking up the story. ‘An agent who apparently had a close relationship with Colin Hutchinson [then Chelsea managing director] told me this when he came to see me and he said. “Chelsea are wondering, if they don't renew, whether next season you'd like to be a player-manager.” That was interesting.’

A few days later, everything fell into place. Gullit was sacked, his high wage demands among the reasons given by the club in a hastily arranged press conference. The news reportedly reached Gullit via Teletext and soon the evening news showed a grinning Vialli being unveiled in his place.

When Gullit gave his version of events for Blue Day, which features interviews with all of Chelsea’s 1997 FA Cup-winning side, he didn’t hold back.

‘It felt like a betrayal by the people around me,’ he said during a chat in the canteen at the club’s Cobham training ground, where he was enjoying a spot of lunch ahead of some work for Dutch television. ‘It was horrible. It was a terrible feeling because it felt like an injustice.’

It may well have been different at the time, but Gullit insists there was no bad blood between him and Vialli. Brilliantly, a week before he was due to be interviewed for Blue Day, the Dutchman had appeared on Italian television alongside Vialli to discuss what had gone on during his final days at Stamford Bridge.

‘Luca was very honest when we spoke about it on TV,’ added Gullit. ‘If somebody says to you, “We are trying to negotiate a new contract [with the manager], but if it doesn't work do you want to be the coach?' is that strange or not?

‘At least you know already what you're doing. So, then he was asked to go to the training ground and he thinks maybe they'll tell him Ruud has extended his contract. Instead it was, “You are the coach now.” He was also surprised. That's why I said I didn't have it with Luca so much. I don't blame Luca.’

The cloud of controversy didn’t linger over Vialli’s head for long. In his first game he instigated a thrilling turnaround against Arsenal in the second leg of the League Cup semi-final, and within six months the club had added that trophy plus two European honours.

Gullit had become yesterday’s news, but he was soon back in the headlines when Newcastle United came calling in need for a replacement for Kenny Dalglish. Despite another FA Cup final appearance, it was a short but not so sweet stay in the North-East, and he left after barely a year in charge. It remains his most recent managerial role in England.

Vialli, meanwhile, led the Blues to a third-place finish in his first full season and then lifted the FA Cup in 2000, before he too was surprisingly shown the door. Like his predecessor, he got back on the saddle soon after, taking charge at Watford, but he didn’t stick around for long and he’s not been near the dugout since.