Page "Agrippina the Younger" Paragraph 5

Antonia Minor was a daughter to Octavia the Younger by her second marriage to triumvir Mark Antony, and Octavia was the second eldest sister and full-blooded sister of Augustus.

Germanicus ’ father, Drusus the Elder, was the second son of the Empress Livia Drusilla by her first marriage to praetor Tiberius Nero, and was the Emperor Tiberius ’ s younger brother and Augustus ’ s stepson.

In the year 9, Augustus ordered and forced Tiberius to adopt Germanicus, who happened to be Tiberius's nephew, as his son and heir.

Germanicus was a favorite of his great-uncle Augustus, who hoped that Germanicus would succeed his uncle Tiberius, who was Augustus's own adopted son and heir.

This in turn meant that Tiberius was also Agrippina's adoptive grandfather in addition to her paternal great-uncle.