The Brazilian centre-back joined the Nerazzurri from Internacional exactly 12 months ago.
"Today is a very important day for me," he posted on his Instagram account. "I've been at the strongest team in the world for a year.
"It is a dream for any player. I have succeeded thanks to hard work. I want to thank Internacional for helping me grow as a player.
"During my first year many good things happened, and I hope that things carry on this way."