He told Chelsea TV: "It was something that happened like a bombshell. The most important thing is to be here and try to project a great future for the club.
"My last year was a year when we achieved so many things and we had support, we had structure with people around me, and now I took this challenge as an individual challenge that I wanted to take.
"It is a big, big step and I am confident that I can respond to Chelsea's expectations and we can focus on the four trophies that we have to win. I am pretty much confident that people will like it. This is a new leadership, a new communication, a new way of being, but I think in the end it all ends up in the motivation everyone must feel to continue to win for the club.
"When I was here before it was excellent times. The move from Porto to London was a brave move for Jose [Mourinho] and it was happy times. We won two Premierships after 50 years from Chelsea winning the first championship and it was something massive by that time, it was something that made us very proud.
"So it is good to be back at a club where I know the people around and hopefully we can start the season with a tremendous impact with staff, players and this new empathy that I want to bring."