Caernarfon Castle, Wales, UK. The Welsh recaptured Gwynedd in 1115, and Caernarfon Castle came into the possession of the Welsh princes. From contemporary documents written at the castle, it is known that Llywelyn the Great occasionally stayed at Caernarfon. Llywelyn ab Iorwerth, (c. 1172 – 11 April 1240) was a Prince of Gwynedd in north Wales and eventually de facto ruler over most of Wales. Llywelyn is generation 27 on family tree.