Lady Forlorn is the ancestral longsword of House Corbray. It has a heart-shaped ruby in its pommel. According to semi-canon sources Lady Forlorn is Valyrian steel. Its dark, smoke-grey steel is reminiscent of Ice, the Valyrian greatsword of House Stark.
First Men King Robar II Royce claimed Lady Forlorn after slaying Qyle Corbray, the Andal King of the Fingers. Robar wielded Lady Forlorn during the battle of the Seven Stars, using it to kill Torgold Tollett and a decoy dressed as Ser Artys Arryn. The Corbrays claim that Ser Jaime Corbray slew Robar in the battle, allowing them to reclaim Lady Forlorn.
At the time of the First Blackfyre Rebellion, Lady Forlorn was wielded by Ser Gwayne Corbray of the Kingsguard. In 196 ᴀᴄ during the battle of the Redgrass Field Gwayne fought Daemon Blackfyre, who wielded the Valyrian sword Blackfyre. Eventually, after nearly an hour of fighting Daemon defeated Ser Gwayne.
An unnamed Lord Corbray wielded Lady Forlorn during the battle of the Trident in 283 ᴀᴄ. When Lord Corbray was wounded, his younger son, Ser Lyn, took up the sword and killed the man who had wounded his father. Lyn then led the charge against the Dornishmen and killed Prince Lewyn Martell of the Kingsguard. Because of this feat the sword was left to Lyn instead of his elder brother Lyonel Corbray when their lord father died.
A Feast for Crows
During Lord Petyr Baelish's meeting with the Lords Declarant at the Eyrie, Ser Lyn Corbray threatens Ser Lothor Brune with Lady Forlorn. Petyr uses the aggression to demand concessions from the Lords Declarant. After they leave, Petyr informs Sansa Stark that Lyn is secretly working on his behalf.
My lady has a thirst. Whenever she comes out to dance, she likes a drop of red.