Fabregas lines up against his former club Arsenal on Sunday, despite the Gunners reportedly having had first option to re-sign the playmaker if he left Barcelona.
Mourinho, who is not aware if Fabregas wanted to return to the Emirates Stadium, said: "The only thing I know is that I spoke with him for the first time and, when I spoke with him, obviously he knew that I was Chelsea manager.
"If he doesn't want to come to Chelsea, I think he refuses to speak with me, he refuses to meet with me.
"When I invited him for the meeting, he told me immediately 'yes'.
"I spoke with him and, after 10 minutes, he was telling me he wants to join us.
"What happened before that, I don't know
What I know is that after that, we did things perfectly.
"He was really happy to join us
After that (meeting), I contacted my club.
"Normally, these things, they take more time, but my club was fantastic."
Mourinho missed a football tournament his son Jose was playing in to meet Fabregas.
The Blues boss added: "My son was in Germany with Fulham and they qualified to play the final against Paris St Germain and I wanted to go
"I never go
And that weekend, I wanted to go but it was the only day that he (Fabregas) could travel to London so I had to stay, to do my job
"No problem, I will watch my son play other times."
While his son's team beat Bayern - "They won 1-0
They won the tournament," the Portuguese added - he was talking to Fabregas about making him the centre-piece of his rejuvenated Chelsea.
Mourinho added: "We spoke about football, we spoke about Chelsea project, we spoke about where I want him to play, the way I want him to transform my team, the Chelsea philosophy also as a club."
There were also general discussions on pay - "not specifically, because this is not my job, but just to give him an idea," Mourinho said - and the response was an unequivocal 'yes'.
In discussions, Mourinho also spoke of Chelsea in comparison to Fabregas' other options, promising the Spain playmaker his versatility would not be used against him, as it appeared it was at times at Barcelona.
"I was objective with him," Mourinho said.
"And I gave him the different possibilities, with me (Chelsea) or playing here or there
'This is the way we want to play', 'this is the way we want to develop the team', 'no way with me you are going to play fake number nine, outside left, outside right - no..
what I need is you to do this, this and this'
"Everything so clear."
Fabregas played 303 times for Arsenal, scoring 57 goals, but Mourinho sees no reason to speak to the former Gunners skipper ahead of Sunday's match.
"I can feel it that it will be another game for him, with that little bit (of emotion) that will be present before the match or in the first couple of minutes, but he played against Barcelona with Arsenal," Mourinho said.
"He is a great professional, the way he behaves, the way he works, a great professional so another professional job for him on Sunday."
Source : PA