It started, as feuds often do, with a misunderstanding. At least that is Watford boss Walter Mazzarri's explanation for why we might expect a frosty air to the greetings when he and Chelsea's Antonio Conte meet for the first time as Premier League managers at Vicarage Road on Saturday.
In 2012, the previously cordial relationship between the men then in charge of Juventus and Napoli, Serie A's two ascendant powers and traditionally bitter rivals, turned on a comment made by Mazzarri.
"There was a certain point when I said that, when they faced us, [Conte] changed the style of play that he believes in, convinced I was paying him a compliment," Mazzarri explained in his autobiography. "I meant to say that he showed adaptability to situations -- it was praise which, instead, was taken badly."
The change Mazzarri was referring to was Conte's shift from a 4-2-4 system at Juventus to a version of the 3-5-2 formation that had powered Napoli's return to the top table of Italian football, by maximising the devastating counterattacking gifts of Edinson Cavani, Ezequiel Lavezzi and Marek Hamsik.
Mazzarri insists he never intended to imply that Conte had copied his tactics, but his words were greeted with disdain by the Juventus boss and his coaching staff.
"I've heard that the current Juve side are meant to be inspired by Mazzarri," Conte said in the autumn of 2012. "Well you can copy numbers, but certainly our mentality and the way we approach games is very different. Then there is the way we always want to take the initiative, our principles... do I need to go on?"
By then the ill feeling had bubbled to the surface during an anything-but-friendly Italian Super Cup clash in Beijing; a match Conte missed while serving a touchline ban for subsequently quashed match-fixing allegations, with assistant Massimo Carrera overseeing things in his absence.
Juventus roared back from 2-1 down to win the match 4-2 after extra time, but only once Goran Pandev, Juan Camilo Zuniga and Mazzarri himself -- outraged at the awarding of a penalty against his side in the 76th minute -- had been sent off by referee Paolo Mazzoleni. At the instruction of their coach, the Napoli players boycotted the trophy presentation.
Asked about Napoli's grievances after the match, Carrera said: "To be honest, what I saw was them doing a manhunt -- when they were ahead, they were obstructing us and the only mistakes we made in the game were for their two goals. I wouldn't know what else to say."
Mazzarri later wrote: "After that final in China, the Juventus coaching team wanted to make out that it had been a deserved win, but I want to emphasise once again that you only win deservedly when it's 11 vs. 11. Even Conte made some unfair and unfortunate comments and I always had doubts as to whether he had been put up to it, maybe by his press officers, looking for the latest controversy. Conte is far better than some of the things he has said in the past."
Indeed, when Conte was the surprise choice to succeed Luigi Delneri as Juventus manager in the summer of 2011, Mazzarri claims he recognised a kindred spirit and was one of the 47-year-old's most strident advocates.
"I could see in him the same attitude that I had at Reggina," Mazzarri wrote of Conte. "When he was appointed by Juventus, I was delighted -- it broke a taboo and proved that if somebody is good enough, then they are good enough anywhere. In fact, his emotional drive could make a difference at the highest level and to be honest, I thought to myself 'I like this guy'."
Conte's star outshone Mazzarri's over three spectacular seasons in Turin, during which Juventus won three consecutive Serie A titles, went an entire league campaign undefeated and set a new record for points won. But matches against the man he believed had publicly slighted him always carried an extra edge.
"No, I never spoke with him," Conte said of Mazzarri after watching his Juventus side play out a 1-1 draw with Napoli at San Paolo in March 2013. "Never, never, never. We didn't even shake hands. I can assure you we didn't even look at each other. Each to their own bench. It's better that way."
It's been more than two years since Conte and Mazzarri shared a touchline, and time may have dulled the dislike.
Circumstances have certainly changed significantly for both men; Mazzarri went to Inter and failed before landing at Watford, while Conte arrived at Chelsea this summer on the crest of a wave, having established himself as the most accomplished coach at Euro 2016 by leading the least talented Italy squad in decades to the quarterfinals with deserved victories over Belgium and Spain.
Now, no longer direct rivals but simply fellow Italians adjusting to life and coaching in England, there should be more in common than divides them. In truth, there were more similarities than differences to begin with.
Nicola Amoruso, a striker who thrived under Mazzarri at Reggina, said of his former boss: "He manages to get the whole team pulling together and he's particularly good at transmitting his enthusiasm and his determination to the players. He's a master at match preparation and he's also a very technical coach who puts in a lot of work on the training field." But he might easily have been talking about Conte.
The Chelsea boss has shown a mellower public face than expected since his arrival at Stamford Bridge, seemingly keen to avoid spats with rival managers that might distract from the more pressing task of reviving an underachieving squad of champions.
Perhaps seeing Mazzarri again at Vicarage Road on Saturday will bring out the beast in Conte. Or perhaps he will simply smile as he looks his former rival in the eye, shake his hand and line his Chelsea team up in a 3-5-2.