Llywarch ap Hyfaidd King Dyfed was born to Hyfaidd Dyfed.
Around 893 Llywarch ap Hyfaidd King Dyfed succeeded King Dyfed.
Around 904 Llywarch ap Hyfaidd King Dyfed was killed by Hywel "Dda aka Good" King Seisyllwg King Deheubarth [aged 24] and his father Cadell ap Rhodri King Seisyllwg [aged 50]. His brother Rhodri succeeded King Dyfed.
[his daughter] Elen Dyfed Queen Consort Seisyllwg Queen Consort Deheubarth was born to Llywarch ap Hyfaidd King Dyfed. She married Hywel "Dda aka Good" King Seisyllwg King Deheubarth.