The phrase "a certain friend of" is correct and usable in written English.
It can be used when referring to a friend in a vague or indirect manner, often to maintain anonymity or to create intrigue.
Example: "A certain friend of mine has been giving me some interesting advice lately."
Alternatives: "an acquaintance of" or "a particular friend of".
Mrs. Engel wants to visit the Sunday Market to find a gift for a certain friend of hers.
I never knew anyone who actually tested this theory, but a certain friend of mine got the time down to single digits.
"There is a certain friend of the president of Russia, he did such and such a thing, and there is probably a corruption element there," Putin said.
With Path search, you can now find all the updates in your network that are tied to a certain friend, place, time of year, birthday, or emotion.
allowing you to reflect on an entire twitter history with a certain friend or revisit a catalog of Instagram photos of you on the beach.
I don't want to sound like a control freak, but I get really irritated when a certain friend makes plans with another of my close friends without including me.
What precisely happened is vague, but a substantial correspondence after May, 1490, in which Ficino asked certain friends of his at the court of Pope Innocent VIII for help, suggests that certain people had called his orthodoxy into question (Kristeller 1956-96, 4 265-76).
There are certain friends of mine who agree with this, the bloody-Mary-at-lunchtime theory.
Her relatives tried to involve certain friends of theirs on the Military Council but the judge resisted and felt perhaps more able to, than he might have in the past.
I had in mind certain friends of mine, who walked in the show but shall remain nameless, with whom I've spent many, many nights getting dressed up in hotel rooms".
And as that happens, we can bask in "Better Now," which Ed performs and which certain friends of mine have likened to Tracy Chapman's "Fast Cars".
