Already putting up some impressive performances for Manchester City since his arrival from Wolfsburg, there’s no denying that Kevin De Bruyne’s importance to Pep Guardiola’s plans has been even more apparent this season, which has brought up the José Mourinho enigma all over again.

Once contracted to Chelsea, the Belgium international never quite made it at Stamford Bridge, and left on the now Manchester United manager’s watch, a riddle that has never really been solved.

When he returned from his loan from Genk after the Blues bought him from the Jupiler Pro League side, the now 26-year-old found himself on the bench very early on, which he wasn’t happy about.

He was the one who made his disappointment public after a preseason game when Roberto Di Matteo failed to give him any time on the pitch, saying: “If my situation doesn’t change, I’m going to need to find a solution. I’m going to need an explanation from the manager.”

A loan to Werder Bremen ensued, where his talent became very apparent, and when he returned, with Mourinho now in charge, people expected him to be a member of the first-team.

Unfortunately, that wasn’t the case, and there’s only so much a footballer can take without being given reasons for his lack of time on the pitch.

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When it became apparent Mourinho wasn’t going to use him and few at Chelsea believed in him, he hit rock bottom.

Patrick de Koster, De Bruyne’s agent, told Sport/Foot this week: “At that time, he was sad, crestfallen. I spent a lot of time in London trying to cheer him up. He only had one question: Why? And no one had an answer for him.”

Despite this, he bounced back, once again in Germany, with Wolfsburg, who bought him from Chelsea for £20m just six months later after an initial loan.

There, he made enough of a name for himself to earn a return to the Premier League, this time with Manchester City, who paid circa £65m for the Belgian.

The rest, as they say, is history, and while José Mourinho has always publicly stood by his decision to not play De Bruyne at Stamford Bridge, there has to be a part of him, somewhere deep inside, that must be thinking “What could have been?”

It will surely be spoken about in the run up to this weekend’s Manchester derby at Old Trafford.