Cybru, Cymru, Kymru
The Welsh name for the Britons who descended from the men of Troy. The Cymry were said to have the divine rights to the island. Arthur was among the members of this race.
Cymry is the correct plural name of the Welsh people, used to refer to the Welsh people collectively. The singular form is Cymro for a Welshman and Cymraes for a Welshwoman. Some suggests it’s synonymous with the Cimmerii and Gomari, while others derive the name from Camber, son of Brutus. And others still tries to thrace it back to Gomer, Japhet’s eldest son.
In the laws of Hywel Dda the name is spelt Cybru, and in G. ap Arthur’s Chronicle the names Kymraec and Kymry are respectively given to the language and the nation.
Cymru is the Welsh name for Wales, pronounced “KUM-ree,” used to denote the country itself.
Source
Triads of the Island of Britain (Welsh ”Triads”) | 11th century to 14th century