De Bruyne spent an unhappy six months at Stamford Bridge under Mourinho, having spent the previous season on loan at Werder Bremen, making just nine appearances - three of which were in the Premier League.
Wolfsburg gave De Bruyne an exit in the January window, and the player has since gone on to become arguably the best midielder in the game at City, and today signed a new contract to extend his stay until 2025.
But it was one pivotal meeting with Mourinho in December 2013 that made De Bruyne make the "best decision to leave Chelsea."
"There was so much in the press about my relationship with Jose Mourinho," De Bruyne explained to Sky Sports last month. "But the truth is that I only ever spoke to him twice. The plan was always for me to go on loan for a bit.
"Jose called me into his office in December, and it was probably the second big life-changing moment for me. He had some papers in front of him, and he said, 'One assist. Zero goals. Ten recoveries'."
"It took me a minute to understand what he was doing. Then he started reading the stats of the other attacking forwards - Willian, Oscar, [Juan] Mata, [Andre] Schurrle. And it's like - five goals, 10 assists, whatever.
"Jose was just kind of waiting for me to say something, and finally I said, 'But... some of these guys have played 15, 20 games. I've only played three. So it's going to be different, no?'
"It was so strange. I was completely honest. I said, 'I feel like the club doesn't really want me here. I want to play football. I'd rather you sell me.'"
De Bruyne went on to win the Germany FA Cup and Supercup with Wolfsburg before moving to City and winning the Premier League twice, FA Cup once and EFL Cup four times.
He added: "I decided to go away because I felt I didn’t have any chances of playing at the time.
"I didn’t see more opportunities coming so for me, it was the best decision to leave Chelsea and go to a situation where I felt I could start again.
"Did I expect it to go this way? Obviously not, because at that time it was a low point in my career but I never had any doubt in my abilities as a football player.
"I can't think what is going to happen eight years down the line playing for City, in World Cups and all that stuff. It's wonderful."