The WikiTree field for his last name at birth (LNAB), Iorweth, needs to be changed. His name is given as Llywelyn ap Iorwerth by both Richardson & FMG, and the Cymru Project's Naming Guide calls for ap/ab/ferch to be included in the LNAB field: ap before a consonant & ab before a vowel sound. A discussion on his profile (see the Notes section) shows that ap is correct:
'in certain circumstances the initial letter "I" in Welsh can sound like a consonant. Thus "Rhys ap Iorwerth" and "Dafydd ap Ieuan". Kind of like in English where an initial "U" can sound like a consonant. We say "a university", not "an university".'
I'm posting here in case that conclusion (ap vice ab) is wrong (and Richardson & FMG are wrong) and it would be better for him to be ab Iorwerth.