https://en.wikipedia.org/wiki/Caesarion
Everyone knows how amazing his father, Julius Caesar, was. But popular culture only remembers on the legendary beauty of his mother. Cleopatra was almost certainly a genius. She could speak 10 languages, and was the first Ptolemy ruler to speak Egyptian (she was actually Greek/Macedonian, the Ptolemy descended directly from Alexanders greatest general). She was educated in math, philosophy and astronomy, introduced Julius Caesar to the astronomer Sosigenes of Alexandria to help create the Julian calendar, and wrote a medical treatise.
Sad that the product of two of histories great geniuses had to be killed by Octavian to protect his claim to the empire. Though the child seldom matches their parents, seems like an irreplaceable genetic loss.
After Germanicus died, the Roman empire went from bad to worse in it's choice of emperors. Tiberius led to Caligula, then Claudius, then Nero, and his death lead to the tumultuous year of the Four emperors.
https://en.wikipedia.org/wiki/Year_of_the_Four_Emperors
From that year comes interesting parallel to Germanicus, the story of Lucius Verginius Rufus.
https://en.wikipedia.org/wiki/Lucius_Verginius_Rufus
He helped put down uprisings by governors intending to become Emperor and twice that year his armies offered to put him on the throne, and he refused both times. In an era where emperors regularly killed anyone who had the political means to be a threat to their throne, he was able to live to the age of 83, where he was again selected as Consul by Emperor Nero.