When someone turns out as an enemy

Question

Imagine a friend in a company who was considered a very reliable guy and after a while others notice that there is a big problem with the guy and he was a sly. All of the friends want him to get out of their company and the guy finds no other way other than leaving the group. Imagine once, all the guys have gathered together and are talking about the past events. There are some newcomers and this is why there is a more tendency to talk about the past sweet happenings. Abruptly, one of the group old members begins to talk about that guy who was kicked out of the group. The old member wants to say that: "in spite of that the guy was in the group for a long time, all of us thought that he was a very loyal and reliable person up to the last minute, but when the story... happened, we got that he is a bad individual because he acted like an enemy not friend."

My question: does the self-made sentence below make sense to you to convey this message?

• He turned out as an enemy.

Meaning that: "he was an enemy, but we didn't know it"

Added: I need to know it my mentioned sentence sounds natural in English and if yes, does it carry the message in my question or not?

Answer 1

You sentence is understandable and can also be stated as

(In the end) he turned out to be an enemy.

The term for such a person is

a frenemy

and is immortalized in the song You Get What You Give by the New Radicals.

Answer 2

"He turned out to be an enemy" is fine, but doesn't really explore the numerous words and phrases that describe someone who becomes an adversary of the people who thought they were his friends.

For example, there are all the words that more or less mean "traitor": turncoat, renegade, deceiver, betrayer, quisling, snake, rat, double-crosser, back-stabber, double-dealer, false friend, Judas, etc., along with their various other forms.

All that time we thought he was our friend, we never expected him to stab us in the back.

That lying, cheating, no-good, snake-in-the-grass. He was just waiting for his chance to turn on us.

"Frenemy", as in Peter's answer, is I think a bit too colloquial for common use. In addition, it can be applied to someone you can't quite trust, but either are compelled to do so anyway, or are forced to do so by circumstance. This is the kind of thing that is the basis for a number of "buddy movies", in which two rivals must work together to defeat some common antagonist -- for example, Sarah Connor and the Terminator must work together in Terminator 2: Judgment Day (1991) to defeat the new T-1000. They're not quite friends, they're not quite enemies -- They're frenemies.