The 24-year-old has joined the Italian club after deciding not to sign a contract extension with Arsenal, saying their failure to succeed in the title race influenced his decision to join the Italian giants.
The Frenchman revealed he may have opted to stay if they had succeeded but said watching the Gunners lose the race after leading their rivals Manchester United by five points, made it too painful for him to remain in North London.
Speaking to News of the World and asked whether winning the league would have influenced his decision, Flamini said: "That would have weighed in the balance. It would certainly have counted.
"I actually wanted to sign a new contract at Arsenal last July but it didn't happen. AC Milan did so much to sign me I couldn't refuse.
"What happened to us after leading the league for so long was the most painful experience I had during four years at Arsenal."