Through his mother Julia, he was a relative of the Julio-Claudian dynasty. He was the grandson of Drusus (only son of Tiberius Caesar), and the great-grandson of Tiberius and his brother Drusus. Through his great-grandmothers Vipsania Agrippina and Antonia Minor, he was also descended from Marcus Vipsanius Agrippa and Mark Antony but not from Augustus.
He was descended from Augustus" sister Octavia Minor, herself a great niece of Julius Caesar.
His father died in 38. His mother was the only daughter of Drusus, and had previously been married to her cousin Nero Caesar, without issue.