The Brazilian took to social media to announce the news:
The news didn't come as a surprise, after the 35-year-old made it clear he wouldn't renew with Orlando City earlier this year, per ESPN FC. At the time, he didn't rule out another spell with Brazilian club Sao Paulo, but retirement always seemed more likely.
Kaka moved to Europe in 2003 to join Milan and enjoyed the best spell of his career in Italy. With the Rossoneri, he won one Serie A title and the UEFA Champions League, and he also added the 2007 Ballon d'Or award―becoming the last to win the trophy before the dominance of Lionel Messi and Cristiano Ronaldo.
When he moved to Real Madrid in 2009, he was widely regarded as one of the best players in the world, but he never lived up to the hype in the Spanish capital. Injuries played their part, but he also proved a poor fit with Los Blancos, who signed Ronaldo in the same window and placed a higher emphasis on pace and athleticism.
He would return to Milan for one season before moving to MLS in 2014. With Orlando, Kaka again showed flashes of his tremendous talent, giving the expansion team an immediate boost.
While his spell in La Liga was short, the league's official Twitter account congratulated the Brazilian on a wonderful career:
Per ESPN FC, Kaka previously told Sky Sport Italia he could return to the Rossoneri in some capacity, and the Italians could certainly use his help. Milan have consistently disappointed for years, failing to live up to the expectations since his second spell with the squad.
He visited the San Siro in November and met with the club's new owners, so don't be surprised if Kaka takes a position with the Rossoneri in the near future.