AC Milan fans never fully took to Hakan Calhanoglu during his four years with the club.
Seeing him join Inter last summer still hurt, though, particularly as he left on a free transfer.
So, when the two city rivals faced off in the Derby della Madonnina last November, the Rossoneri faithful whistled and booed their former attacking midfielder's first few touches.
Hakan, though, replied in the best possible fashion, at least from Inter's perspective, by converting a 10th-minute penalty.
However, his subsequent celebration caused controversy, as he stood in front of the Curva Sud and cupped his ears.
For some, like Borja Valero, it was a fitting riposte, with the former Inter playmaker arguing on DAZN that he deserved credit for having the "courage" to take the spot-kick.
For others, such as Sportmediaset pundit Alessio Tacchinardi, it was "disrespectful".
Alessio Florenzi was certainly unimpressed. The Milan substitute even took a few steps onto the pitch at San Siro to remonstrate with Hakan.
In the run-up to Saturday evening's return clash, where Inter will be the designated home team at their shared stadium in San Siro, Milan defender Davide Calabria insisted that neither he nor any of his team-mates were "personally" offended by Hakan's celebration.
As far as Stefano Pioli's squad are concerned, there are no hard feelings.
Unsurprisingly, though, many Milan supporters see things rather differently.
They were enraged by Hakan's actions (the player also took to Instagram after the game to declare his commitment to the Inter cause alongside a video of his goal).
Indeed, the Curva Sud ultras went so far as to hang an offensive banner across the city's Ponte del Portello bridge the following day.
It read: "Courage is not taking a penalty kick after 10 minutes, but remaining with your wife after she cheated on you."
It was all rather distasteful and felt utterly unnecessary.
As Hakan himself has pointed out, several players have previously crossed the Milan divide without being subjected to anything like the same hostility.
"It's normal the fans are upset, but I am not the first to do this and I won't be the last," he told DAZN.
"I just wanted to look to my future, with all due respect to Milan. I did a lot for Milan over four years, I respected everyone, but I have a new chapter at Inter and have to look forward now."
However, Hakan hardly helped matters with some of the comments he made shortly after leaving his former club.
There was a pointed reference to his trophy-less time at Milan when he said that one of the reasons he joined Inter was that he wanted to "win something in Italy".
He also explained that he knew that Inter were "a great team" because "they often beat Milan in derbies".
Hakan has also publicly alleged that the Rossoneri didn't really want to keep him, even though they offered him a contract extension worth €4 million (£3.4m/$4.6m) a season.
“Pioli was the only one who really wanted me at Milan," he claimed. "I spoke to him many times, but he respected my decision and wished me all the best."
Whatever the truth about the nature of his departure, Milan's loss is proving Inter's gain.
Whereas Brahim Diaz is now struggling at Milan after a bright start to the season, Hakan's Inter career has taken off after his derby goal.
Indeed, he had scored just once going into the 1-1 draw at San Siro, and even that had been on the opening day of the season, in a 4-0 rout of Genoa.
However, the 27-year-old now has six goals, and seven assists, to his name.
There had been some doubt over how he would fare at Inter.
Part of the reason why he had never been fully embraced by Milan fans was his maddening inconsistency.
It was only after the arrival of Pioli, who played him as a No.10 in his preferred 4-2-3-1 formation, that he began to deliver on a regular basis.
Simone Inzaghi obviously favours a 3-5-2 formation but Hakan has belatedly grown into the role that Luis Alberto played for the former Lazio boss at the Stadio Olimpico.
As one of the cleanest strikers of a ball in the game today, Hakan has also added another weapon to Inter's arsenal.
The Nerazzurri scored the joint-most headed goals in Serie A last season, with 14 – they've already matched that tally this term.
Inter have also netted more headed goals (16) than any other side in Europe's Big Five leagues, and Hakan's deliveries are one of the many reasons why.
He ranks No.1 in Serie A this season for dead-ball assists (five), chances created from set plays (27) and successful corners (29).
In a game like Saturday's, which should be typically tight and tense, do not be surprised if a Hakan cross proves crucial.
How he celebrates any goal will obviously be of great interest to the Milan fans in attendance.
But make no mistake about it: Pioli and his players will not be focusing right now on how disrespectful Hakan might be – but rather how dangerous he will be with a dead ball.