Ferrex was a legendary king of the Britons as accounted by Geoffrey of Monmouth

Geoffrey of Monmouth

Geoffrey of Monmouth was a cleric and one of the major figures in the development of British historiography and the popularity of tales of King Arthur...

. He was the son of Gorboduc

Gorboduc

Gorboduc was a legendary king of the Britons as accounted by Geoffrey of Monmouth. He was married to Judon. At an old age, he became senile and his sons, Ferrex and Porrex, feuded over who would take over the kingdom...

 and Judon.

When his father had become old, he waged war on his brother, Porrex

Porrex I

Porrex I was a legendary king of the Britons as accounted by Geoffrey of Monmouth. He was the son of Gorboduc and his death began a dynastic civil war....

, for who would succeed to the kingship. He fled to Gaul

Gaul

Gaul was a region of Western Europe during the Iron Age and Roman era, encompassing present day France, Luxembourg and Belgium, most of Switzerland, the western part of Northern Italy, as well as the parts of the Netherlands and Germany on the left bank of the Rhine. The Gauls were the speakers of...

 and enlisted the help of Suhard, the king of the Franks

Franks

The Franks were a confederation of Germanic tribes first attested in the third century AD as living north and east of the Lower Rhine River. From the third to fifth centuries some Franks raided Roman territory while other Franks joined the Roman troops in Gaul. Only the Salian Franks formed a...

. Upon his return, he fought a battle with his brother and died there. The Gaulish army was also destroyed. His mother, Judon, avenged his death by killing Porrex in his sleep some time later. This led to a civil war for some time in Britain

Great Britain

Great Britain or Britain is an island situated to the northwest of Continental Europe. It is the ninth largest island in the world, and the largest European island, as well as the largest of the British Isles...

.