Kaka left Milan for Real Madrid in 2009, but after being deemed surplus to requirements at the Santiago Bernabeu agreed a second spell with the Rossoneri earlier today.
The 31-year-old admitted that his desire to make Brazil's squad for next summer's World Cup was a driving factor behind the move, which he feels suits both parties.
He told the Milan Channel: "It has been two weeks that I thought I could come back. In the last few days, I've been dreaming of hearing the fans sing my name in the San Siro again.
"Four years have passed and now I'm back. A return to Milan is the ideal for me. I have a lot of desire to play and it's a very important year for me due to the World Cup, but right now I just want to do well for Milan, my team.
"I was very sad to leave this club and now it's great to be back. I'm very happy."
Kaka spent six seasons with Milan during his first spell in Serie A, scoring 95 times in 270 appearances in the process.