Eto'o was reunited with Mourinho when he joined Chelsea from Russian side Anzhi Makhachkala on a one year deal at the end of August.
It was a move Eto'o himself would once have never have agreed to.
"Before meeting up at Inter, Jose and I didn't know each other personally, so our relationship was a little tense," he said in an interview with The Sun.
"I think I even said one time that I’d never play for a club where Jose was coach.
“But God knows best. He wanted to show me that I was wrong and today Jose is a friend. Now he’s my coach again.”
He added: "It's a real pleasure to team up with him again. He's as good on the pitch as outside of it, and this is a real and rare quality for a manager."
The Cameroon international also rubbished suggestions he left Inter Milan for Anzhi for financial reasons.
"When I went to Anzhi, people said it was for the money, but it was for the challenge," he said. "The challenge at Anzhi was to bring a team at the bottom to the top, and that's what I did.
"At Chelsea, I'll have the opportunity to play with proven and established players."
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