From the Council of Toledo, A.D. 655

Canon X. Whoever from bishop down to subdeacon, being constituted in honor, hereafter shall have procreated sons either from a female slave or from a free woman in a detestable union, those indeed from whom they are proved to have been begotten are to be condemned by canonical censure; but the offspring born of such pollution shall not only nowhere receive the inheritance of the parents, but shall also remain by perpetual right in servitude to that Church from whose priest or minister's disgrace they were born.

Since the offspring is considered as illegitimate, these Fathers seem to have held those nuptials not only illicit but invalid.