Middle English for-, fore-, from Old English fore-, often for- or foran-, from fore (adv. & prep.), which was used as a prefix in Old English as in other Germanic languages with a sense of "before in time, rank, position," etc., or designating the front part or earliest time.
"make mention of, speak of briefly or cursorily," 1520s, from mention (n.) or else from French mentionner, from Old French mencion. Related: Mentioned; mentioning. Not to mention as a "rhetorical suggestion that the speaker is refraining from presenting the full strength of his case" [OED] is by 1690s. Don't mention it as a conventional reply to expressions of gratitude or apology is attested from 1840.
<a href="https://www.etymonline.com/word/fore-mentioned">Etymology of fore-mentioned by etymonline</a>
Harper, D. (n.d.). Etymology of fore-mentioned. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/fore-mentioned