His grandfather was a member of the Welsh Royal House of Gwynedd, and Owain was very aware of his dynastic hereditary claim as the last living male of Llywelyn's family.

Another of Llywelyn's brothers, Rhodri ap Gruffydd, renounced his rights in Gwynedd and spent much of his life in England as a royal pensioner.

Lawgoch left again for France in March 1366 and was in French service by 1369 (hostilities in the war were suspended between 1360 and 1369), but adhering to the enemy had his lands in Wales and England confiscated.

[6] He was however deprived of his English lands in 1369, suggesting he was in the service of the French as leader of a Free Company when the period of truce between France and England following the Treaty of Brétigny ended and hostilities resumed in 1369.

[8] The second in command of this company was Ieuan Wyn, known to the French as le Poursuivant d'Amour, a descendant of Ednyfed Fychan, Seneschal of Gwynedd under Owain's ancestors.

[8] Welsh soldiery and longbowmen who had fought for Edward I in his campaigns in North Wales remained armed and sold their services to the English kings in their battles in Scotland and at Crecy and Poitiers.

The alarmed English government sent an agent, the Scot John Lamb, to assassinate Owain, who had been given the task of besieging Mortagne-sur-Gironde in Poitou.

[12][5] The Issue Roll of the Exchequer dated 4 December 1378 records "To John Lamb, an esquire from Scotland, because he lately killed Owynn de Gales, a rebel and enemy of the King in France ...