Aegon Blackfyre

Aemon Blackfyre is an unseen character in Game of Thrones. He is not expected to appear in the series, being long dead by the time it begins.

Background
Aegon Blackfyre was the firstborn son of Daemon Blackfyre, a legitimized bastard son of King Aegon IV Targaryen and his cousin Daena Targaryen, by Serena Blackfyre. He had two brothers: Aemon, his twin, and Daemon II Blackfyre.

Season 1
Aegon, along with his siblings is mentioned in the House Targaryen's entry of the book The Lineages and Histories of the Great Houses of the Seven Kingdoms.

In the books
In the A Song of Ice and Fire novels, Aegon was Daemon Blackfyre's heir and squire.