Daemon III Blackfyre

"When Haegon was executed, Bittersteel crowned Haegon's elder son Daemon III, who, in turn, was slain by the Lord Commander of the Kingsguard, Ser Duncan the Tall."

- Varys

Daemon III Blackfyre was the elder son of Haegon Blackfyre and a pretender to the Iron Throne.

Biography
Bittersteel crowned Daemon king after the death of Haegon. During his rebellion, Daemon was killed by Ser Duncan the Tall.

In the books
In The World of Ice & Fire, Daemon invaded Westeros with the Golden Company, starting with a landing on Massey's Hook. He had precious few supporters. Daemon was slain by Ser Duncan the Tall at the Battle of Wendwater Bridge.