Torres switched from Liverpool to Chelsea in a then-British transfer record £50million deal in January 2011.
Despite winning a UEFA Champions League, Europa League and FA Cup with the club, he never found the form he showed at Anfield and, after Chelsea recruited Costa this summer, Torres knew he needed to move on.
He is now relishing helping Milan get back to the top in Serie A after moving to the San Siro on a two-year loan.
“Obviously I could see what the season at Chelsea was going to be. They signed a striker that was expecting to play and I need to have this feeling of being important,” said Torres at his unveiling in Italy.
"I want to thank my two English clubs, Liverpool for bringing me to the Premier League and Chelsea for the trophies I won.
“After all these years, however, I needed a change, something that would give me the desire to play, to feel important.
“AC Milan is all I needed, a great club with great fans where I will try to shine and come back myself. We need to return to the first three (Serie A teams) and I want to get back my past levels.
“I'm happy to be here, I can't wait to begin. I played in La Liga and in the Premier League, now I am in the third most important league in Europe.”
He added his relationship with former Inter Milan and current Chelsea boss Jose Mourinho was professional and he left on good terms.
“I learned so much with him, maybe in the future our paths can meet in again," he added.
“When I told him about AC Milan he wished me good luck, he talked to me about the passion there is here (in Milan). I wish him the best as he did with me.”
Torres replaces another big-name striker Mario Balotelli at the San Siro after the Italy international joined the Spaniard's former club Liverpool.
“Balotelli? He was important here, I wish him good luck for his new experience with Liverpool."