Mourinho sold De Bruyne to Wolfsburg for a deal worth £18million in January 2014 and the Belgian has blossomed in Germany, helping his new club to second in the Bundesliga last season with 10 goals and 22 assists.
His excellent form has reportedly attracted interest from a host of top clubs in Europe including Manchester City, who are thought to be ready to pay more than £50million to land the 24-year-old.
De Bruyne has claimed he was never given a chance to impress at Chelsea, where he made just three appearances in the league, but Mourinho maintains it was the player's decision to quit Stamford Bridge.
"That is unfair because I wanted to keep him and he told me it was not in his personality to be competing for a position in the team," Mourinho told national newspapers.
"He needed a team where he knows he can play every game
He needs to know that he is important.
"He did not want a team where he thinks, 'am I playing or not?'
He needs that trust, he needs that quality
He needs that security
So I was not happy when he left
So yes it's not fair."
Mourinho added: "He was not training very well and he was saying, 'I can't give you more - this is just my way'.
"So yes, I accept that if this is his mentality and it's his choice to go, it is better for Chelsea to make a good deal.
"Chelsea made a good deal and he was happy to go and I am happy because the kid is a good kid."
Chelsea took a considerable profit on De Bruyne, having signed the youngster for £6.7million from Genk, and Mourinho says he will feel no disappointment if he lines up for City this season.
"Players have different circumstances," Mourinho said.
"We sold him, made our money and it was fantastic because we bought him cheap and sold him for a fantastic price.
"And now Wolfsburg, if they make a fantastic deal, that is good for them."
Source : PA
Source: PA