Grainne was the daughter of Cormac MacAirt, the High King of Ireland and the most beautiful woman in Ireland. Courted by many, she was to be wed with Chief Fionn MacCool, a famous hunter and warrior. However the age of Chief MacCool, who was older than Grainne’s father, repulsed her, and at their wedding feast she noticed a young warrior - Diarmuid Ua Duibhne, who served under Fionn. Diarmuid had a magical love spot on his right cheek, causing any woman who looked at it to fall in love with him, and Grainne did just that – nullifying any resistance Diarmuid showed out of loyalty to his Chief with a geis – a curse that made Diarmuid follow Grainne and run away with her. Having previously drugged the whole crowd, the eloping couple ran all across Ireland, hotly pursued by a very angry Fionn and his men. There are caves, trees and all kinds of nooks and crannies, under or inside of which local legend has it that Diarmuid and Grainne lay together and hid.
After long years on the run, Grainne fell pregnant with Diarmuid's child. One day out in the wilderness, with Fionn and his men closing in, Diarmuid and Grainne came across the heath of Benbulben where a giant boar confronted them. This was bad news for Diarmuid, for legend tells that the only living creature that could harm him was a wild boar. As the boar charged, Diarmuid, protecting his heavily pregnant lover, wrestled it to the ground in a fight to the death. The warrior killed the boar with his sword, but not before the boar had gored Diarmuid, fatally wounding him. Having caught up, Fionn could have saved his dying comrade simply by letting him drink water from his hands, but he let the water slip through his fingers.