Silva has signed for Gremio on a contract until December 2023, four months after leaving Real.
Real released Silva from his contract in September and he has found a new club as a free agent, earning a four-year deal at Gremio.
"I take great pride and great satisfaction in accepting the challenge of wearing this great shirt of Brazilian and world football," Silva posted on Twitter.
"Thank you for your confidence and be sure there will be no lack of commitment, dedication and hard work."
Silva will join up with his new team-mates in Porto Alegre on 8 January.
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