Balotelli is expected to agree a four-and-a-half year deal with the Serie A giants later today after the two clubs settled on a suitable transfer fee yesterday.
Mancini has revealed that he treated Balotelli like a member of his family and conceded that he spent extra time trying to nurture the volatile forward's talent.
He told The Sun: "We are so sad because Mario was an important player for us. With Mario we won the Premier League and the FA Cup in two years.
"It was difficult because he could be important in the next 14 games. But it's important for Mario to go back to Italy. For me, Mario was like another one of my children. You can be upset with him but afterwards he's a lovely lad.
"I invest a lot of time with all players. With Mario, maybe more. It was emotional when we said goodbye. When I say that I love Mario, and all his teammates love him, it's true."
In their first game without Balotelli last night, City were held to a goalless draw by Queens Park Rangers.