Nicene and Post-Nicene Fathers, Ser. II, Vol. XIV:
The Canons of the Council in Trullo; Often Called The Quinisext Council.: Canon XCVIII

Canon XCVIII.

He who brings to the intercourse of marriage a woman who is betrothed to another man who is still alive, is to lie under the charge of adultery.

p. 407 Notes.

Ancient Epitome of Canon XCVIII.

He is an adulterer who takes one espoused to some one else.

Aristenus’s commentary on this canon is Σαφής.  A more extraordinary estimate of it could hardly be made.  So far from the meaning being “perspicuous,” as the Latin translation has it, the meaning seems to be past finding out; for, as Van Espen remarks, a man who sins with a betrothed woman is certainly not an “adulterer.”  He tries therefore to introduce the idea that though he is not an adulterer, yet he is to be punished as if he were.  But the Greek hardly seems patient of this meaning, and the Ancient Epitome says in so many words that he is an adulterer.

On account of this difficulty some have supposed that the espousals here mentioned were not de futuro but de prœsenti, and that therefore it was the case of stealing a real wife of another man.  But this explanation also is involved in many difficulties.