"It will be exciting to play with Kaka. He is among the best in the world. He is also a friend and we play well together," he said.
Ronaldinho underwent a medical in Milan on Wednesday and signed a contract that will keep him at the Serie A club to the end of the 2010-11 season.
City had reportedly bid £25.5m for the player, but AC Milan are believed to have paid considerably less for him.
Rossoneri fans snapped up 5,230 season tickets on Wednesday alone, following news of Ronaldinho's imminent arrival.
Manchester City boss Mark Hughes said his disappointment at missing out on the star had been eased by the club's show of ambition.
"We presented our case as well as we possibly could and the fact that we are in there trying to get one of the top players in the world shows where we want to go," he said.
"I don't know the finer details of the negotiations, but the way the Ronaldinho deal was constructed was a little bit different by all accounts to an ordinary deal, so my budget would not have been affected as much as people think."
Reports suggested that Ronaldinho's negotiating team were ultimately unimpressed by a financial package from City that was heavily weighted with clauses relating to performance, success and marketing.
Italian newspaper Gazzetta dello Sport reported that Milan will pay Barcelona just £14.6m for his services, with the figure likely to be increased by performance-related bonuses.
The two-time Fifa World Player of the Year's time at Barcelona effectively came to an end in June when new manager Pep Guardiola announced the playmaker was surplus to requirements.
Ronaldinho helped Barcelona win back-to-back Spanish league titles (2004-05, 2005-06) and the Champions League in 2006, but failed to cement a regular place in the starting XI last season because of injury and fitness problems.
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