It was the most vicious feud in Premier League history but Antonio Conte and Jose Mourinho claim to have since buried the hatchet ahead of Sunday's showdown.
Mourinho refers to Conte as a clown, Conte suggests Mourinho has dementia, Mourinho brings up Conte's match-fixing allegations... it was a feud that got positively ugly between the two rival managers.
And though Mourinho insists the pair cleared the air with a meeting after Chelsea's most recent visit to Old Trafford, that period of detente will be pushed to the limits with Sunday's high-pressure FA Cup final meeting.
On the pitch the pair have met six times across their managerial careers, spanning their spells in both the Serie A and the Premier League.
Their first meeting came when Mourinho took his table-topping Inter Milan side to visit Conte's struggling Atalanta at the Bergamo.
Mourinho's men took the lead through Diego Milito and later hit the post as they completely dominated their opponents. But Wesley Sneijder was later sent off and Atalanta would score nine minutes from time to rescue an unlikely point.
Though their teams did battle on the field, both managers were serving touchline bans for the clash and therefore watched on from the stands. Mourinho's for sarcastically applauding a referee in the previous match.
It proved a minor blip for Inter in their treble-winning campaign but the feisty affair sparked Mourinho and Conte's feud into life and reignited almost seven years later when they renewed hostilities in England.
Struggling during his first campaign as Manchester United boss, Mourinho's return to Stamford Bridge was a chastening experience as his former club emerged 4-0 winners.
Mourinho took exception to Conte's frenzied celebrations after Chelsea's fourth goal and his frustration boiled over at the final whistle as he accused his counterpart of trying to humiliate his team after the final whistle.
The incident left a bad taste in Mourinho's mouth and the animosity only increased when Chelsea beat United 1-0 in the FA Cup four months later with N'Golo Kante scoring the only goal of the game.
The pair had to be separated by the fourth official Mike Jones on the Stamford Bridge touchline during a particular flash point.
Conte was infuriated by the harsh treatment Eden Hazard received from some of United's defenders and accused Mourinho of setting up his team to deliberately try and kick the Belgian after the match.
It was then that the war of words truly escalated. Conte painted Chelsea as the underdog and labelled United as big-spending under achievers.
Mourinho's response was a cheeky yet personal jibe as he referenced the Italian's miraculous hair regrowth, saying: 'I'm not going to lose my hair to speak about Conte'.
At the turn of the year, Mourinho responded to a question about his lack of visible passion on the touchline by suggesting animated celebrations are akin to 'behaving like a clown'. just as Conte had done in their first Premier League clash.
'I think he has to see himself in the past, maybe he was speaking about himself in the past, yeah?' Conte said when asked about Mourinho's 'clown' comments.
'Maybe sometimes, someone forgets what they said or his behaviour and sometimes I think there is, I don't know the name, demenza senile, when you are a bit [taps the side of his head].'
Never one to be outgunned in a managerial feud, Mourinho delved deep into the Italian's past by bringing up Conte's match-fixing allegations.
The then-Juventus boss served a four-month suspension - reduced from an initial 10 months - in 2012-13 for failing to report match-fixing at his previous club Siena. He was later cleared of any wrongdoing.
Clearly upset by Mourinho's remarks, Conte defended his record and described the Portuguese as 'a little man' for delivering such a low blow.
The Chelsea boss would have the last laugh by winning the Premier League title as United finished in sixth.
Mourinho would finally get the better of his counterpart in their next meeting, a 2-0 victory at Old Trafford after which Conte admitted the best team had won.
His graciousness in defeat was perhaps due to Chelsea's position at the time. The loss was a mere speeding ticket en route to the Blues' dominant Premier League title success.
Their rivalry rolled into 2017-18 as Mourinho endured another unhappy return to Stamford Bridge when Alvaro Morata's header settled a November contest in the Blues' favour.
Mourinho's men would hit back to secure his second win over Conte in February's 2-1 victory at Old Trafford, secured with Jesse Lingard's winner off the bench.
The United boss explained that the pair got 'bored' by the feud so decided to shake hands and talk it over in his Old Trafford office after the match.
But with Mourinho desperate to win a trophy after a season of being overshadowed by United's city rivals and Conte prepared for one last swing before his likely departure, those niceties will be tested to the limit on Sunday.