Council of Trent: Session XXIV, Reformation of Marriage, Chapter IV

CHAPTER IV. Affinity arising from fornication is confined to the second degree.

Moreover, the holy Synod, moved by the same and other most weighty reasons, limits, to those only who are connected in the first and second degree, the impediment contracted by affinity arising from fornication, and which dissolves the marriage that may have been afterwards contracted. It ordains that, as regards degrees more remote, this kind of affinity does not dissolve the marriage that may have been afterwards contracted.

Translation: J. Waterworth, The Canons and Decrees of the Council of Trent (1848), Hanover Historical Texts Project transcription (1995).