This was always an issue in Rome. People were afraid their heirs would turn out to secretly be wannabe dictators, and you couldn't do anything about it since you were dead. How would you go about making sure your heir was as close to your vision as possible, both outwardly and in their desires should they be emperor?
I would probably keep my nephew in my summer palace after murdering his dad for being too popular and then killing the rest of our family around him. Caligula turned out well, although to be fair I only read up to his first year as Emperor...