Haegon Blackfyre

"Then another son, Haegon, crowned by Bittersteel, another legitimized bastard who had founded the Golden Company to support the Blackfyre claim."

- Varys

Haegon Blackfyre was a son of Daemon I Blackfyre. He had at least two sons, including Daemon III Blackfyre, the elder.

Biography
Sometime after the death of his brother Daemon II, Haegon was crowned king by his uncle Bittersteel. This rebellion failed, and Haegon was executed.

In the books
In The World of Ice & Fire, Haegon and Bittersteel went into exile in Tyrosh after the Battle of the Redgrass Field. During the Third Blackfyre Rebellion of 219 AC, Haegon was dishonorably killed after surrendering.