Rashi on Leviticus 21:15/רש"י על ויקרא כ״א:ט״ו

1ולא יחלל זרעו NEITHER SHALL HE PROFANE HIS SEED — ,thus if he marries one of these women disqualified for a union with him his offspring (זרעו) from her becomes “profaned" (חלל) being exempted from the general law of holiness that applies to the priestly status (cf. Kiddushin 77a).