From the interview to Il Corriere della Sera Read it all here
Luciano Fontana: One last question. What is your biggest regret in life? What do you consider a mistake that you would never want to make again?
Vladimir Putin: I will be quite frank with you. I cannot recollect anything of the kind. By the grace of God, I have nothing to regret in my life.
Question: You are a happy person.
Vladimir Putin: I am, thank God.