Abergwyngregyn is a village and community of historical note in Gwynedd, a county and principal area in Wales. Under its historic name of Aber Garth Celyn it was the seat of Llywelyn ap Gruffudd. It lies in the historic county of Caernarfonshire.

Llywelyn ap Gruffudd, Llywelyn II, also known as Llywelyn the Last, was the prince of Gwynedd, and later was recognised as the prince of Wales from 1258 until his death at Cilmeri in 1282. Llywelyn was the son of Gruffydd ap Llywelyn Fawr and grandson of Llywelyn the Great, and he was one of the last native and independent princes of Wales before its conquest by Edward I of England and English rule in Wales that followed, until Owain Glyndŵr held the title during the Welsh Revolt of 1400–1415.