Page "Fëanor" Paragraph 15

However, the true dangers of the oath became apparent when the lovers Beren and Lúthien recovered one of the jewels from Morgoth, which ultimately came into the possession of Dior, their son, who ruled after his grandfather Thingol in Menegroth.

The presence of the Silmaril awoke the oath and caused the brothers to make war on the Elves of Doriath because Dior refused to yield the jewel.

The brothers attacked Doriath, killed Dior and sacked the halls of the Sindar, committing the second Kinslaying.

However, the Silmaril escaped the destruction of Doriath and the oath drove the sons onwards.

When they learned that it was possessed by Elwing daughter of Dior, who dwelt near the mouths of Sirion together with exiles from Doriath and the city of Gondolin, they attacked the place ( after Elwing also refused to return the Silmaril to them ), committing the third and most terrible Kinslaying.

All seven of the brothers survived even the complete rout of their forces at the Nirnaeth Arnoediad, but three of the brothers — Caranthir, Curufin, and Celegorm — died in the second sacking of Menegroth.

At the third and final Kinslaying, the twins Amrad and Amros were slain.