From A Wiki of Ice and Fire
- This article is about the Valyrian steel sword. For the house founded by Daemon Blackfyre, see House Blackfyre.
Blackfyre was passed from Targaryen king to king, until Aegon the Unworthy chose to bestow it on his bastard son Daemon instead of his legitimate son, Daeron, whom he suspected was actually fathered by his brother, Prince Aemon the Dragonknight. 
Some felt that the sword symbolized the monarchy, so the gift was the seed from which the Blackfyre Rebellion grew.
During the Blackfyre Rebellion Daemon continued to wield the sword in battle, and fought an epic duel with Ser Gwayne Corbray of the Kingsguard at the Battle of the Redgrass Field, pitted against Gwayne's own Valyrian blade Lady Forlorn.
After the death of Daemon Blackfyre and his twin sons on the Redgrass Fields, his half brother Bittersteel took Blackfyre with him in exile to the Free Cities, where Bittersteel and Daemon's surviving kin founded the mercenary force known as the Golden Company.
The sword's current whereabouts are unknown.