Aegon Targaryen (son of Rhaegar and Elia)

Aegon Targaryen, is an unseen character in Game of Thrones. He is deceased when the events of the series begin and is not expected to appear in the series.

Background
Aegon Targaryen was the son of Prince Rhaegar Targaryen and Elia Targaryen. He had an older sister, Rhaenys. House Targaryen was deposed as the ruling house of Westeros during Robert's Rebellion. Rhaegar was killed during the fighting and Elia and both their children were killed soon afterwards during the Sack of King's Landing.

In the books
In the Song of Ice and Fire novels, Aegon is the infant son of Prince Rhaegar Targaryen and Elia Martell and died in the Sack of King's Landing.